Curable composition, cured product thereof, optical member and optical device

ABSTRACT

An object of the present invention is to provide a curable composition that can be cured satisfactorily and can form a cured product having a high glass transition temperature as maintained and having high mechanical strength. A curable composition includes a siloxane (A), a cycloaliphatic epoxide (B), and a curing agent (C). The siloxane (A) contains at least two epoxy groups per molecule. The cycloaliphatic epoxide (B) in the curable composition is preferably a compound represented by Formula (I): 
                         
wherein X is selected from a single bond and a linkage group.

TECHNICAL FIELD

The present invention relates to curable compositions each including asiloxane and a cycloaliphatic epoxide. The present invention alsorelates to cured products of the curable compositions, compositions foroptical element formation, and optical elements and optical devicesobtained using the compositions for optical element formation.

The present invention also relates to curable compositions suitable forwafer-level lens preparation (curable composition for a wafer-levellens), and wafer-level lenses and optical devices obtained using thecurable composition for a wafer-level lens.

BACKGROUND ART

Glass materials have been used in application fields such as lenses,prisms, optical filters, mobile devices, and display devices. In theseapplication fields, the substitution of such glass materials with resinmaterials has been actively considered. Among them, curable resinmaterials that have excellent heat resistance (thermal stability) andstrengths receive attention and are increasingly applied to a variety ofuses. Under these circumstances, there is a need for curable resinmaterials excellent in all required properties such as curability, heatresistance (glass transition temperature), and mechanical strength.

Of the curable resin materials, cycloaliphatic epoxides are exemplifiedas materials having excellent curability, and a variety of ways has beenattempted to allow cured products of the cycloaliphatic epoxides to havestill better heat resistance (higher glass transition temperature)and/or higher mechanical strength. In a considered way so as to allow acured product to have higher mechanical strength, a glycidyl-containingcompound and/or an oxetanyl-containing compound is incorporated into acycloaliphatic epoxide. In general, however, the resulting material hasinferior curability upon the incorporation of a glycidyl-containingcompound. The resulting material gives a cured product having a lowerglass transition temperature upon the incorporation of anoxetanyl-containing compound, although the material exhibits bettercurability. It is difficult to improve the mechanical strength whilemaintaining the curability and the glass transition temperature atsatisfactory levels.

Independently, a variety of attempts have been made to use siliconematerials in curable resin materials so as to allow the materials tohave better properties. Typically, a known curable composition includesa silicone material, an organic compound, a hydrosilylation catalyst,and fine polymer particles. The silicone material is a compoundcontaining at least two SiH groups per molecule. The organic compoundhas a triallyl isocyanurate structure and contains carbon-carbon doublebonds that are reactive with the SiH groups (see Patent Literature (PTL)1). A known thermosetting resin composition includes a polysiloxane, anaromatic-ring-containing epoxy resin, and a curing agent. Thepolysiloxane contains a reactive cyclic ether group and contains D unitsand T units in a random form. The D units are derived from anaromatic-ring-containing dialkoxysilane. The T units are derived from atrialkoxysilane containing a a reactive cyclic ether group (see PTL 2).Independently, a known optical resin composition includes asilsesquioxane derivative, an alicyclic-skeleton-containing epoxy resin,and a curing agent and gives an optical component having an Abbe number55 of or more. The silsesquioxane derivative has a random structureand/or a ladder-like structure (either one or both of a random structureand a ladder-like structure) and is obtained by hydrolyticallycondensing an alkyl- or aryl-containing trialkoxysilane with anepoxy-containing trialkoxysilane (see PTL 3).

All the citations, however, fail to disclose a way to allow acomposition to give a cured product having higher mechanical strengthwhile maintaining excellent curability of the composition and a highglass transition temperature of the cured product.

Recent electronic products have had dramatically decreasing size andweight and dramatically increasing performance. Such electronic productsare represented by mobile phones, smartphones, tablet terminals, mobilecomputers, personal digital assistants (PDAs), and digital still cameras(DSCs). With the technological trend, demands have been increasinglymade to reduce the size, weight, and thickness of lenses for usetypically in cameras to be mounted to these electronic products. To meetthe demands, wafer-level lenses have been used increasingly.

Imagers typically of cameras have an increasing number of pictureelements. This necessitates lenses having such a high resolving power asto support the increasing number of picture elements and employs, forexample, cemented lenses each including a stack of two or more lenses.The wafer-level lenses are suitable for such uses. In general, lenseshave different refractive indices for different wavelengths of light andundergo chromatic aberration. The chromatic aberration is a phenomenonin which displacements (halation or blur) occur in the image. To reducethe influence of the chromatic aberration, regular lenses have astructure in which a lens having a high Abbe number is used incombination with a lens having a low Abbe number to compensate thechromatic aberration. Of lens glass for use in cameras, glass having anAbbe number of 50 or less and glass having an Abbe number of 50 or moreare respectively called flint glass and crown glass.

As materials for the wafer-level lenses, curable resin materials thathave excellent heat resistance and strengths receive attention. Toefficiently produce high-quality wafer-level lenses, demands are made toprovide curable resin materials that excel in all of curability, heatresistance (e.g., a glass transition temperature), and mechanicalstrength. Curable resin materials, if being inferior in any of theseproperties, may adversely affect the quality and/or productivity of theresulting wafer-level lenses. For example, a curable resin materialhaving poor curability requires a long time to undergo a molding processand suffers from inferior productivity. A curable resin material havinga low glass transition temperature suffers typically from sagging andcauses the resulting lens to have inferior shape precision (dimensionalprecision). A curable resin material having a low mechanical strengthsuffers from cracking upon releasing from the mold.

The curable resin materials are exemplified by epoxides that exceltypically in electrical properties, water-vapor resistance, and heatresistance. Among them, cycloaliphatic epoxides are materials excellenttypically in electrical properties, water-vapor resistance, heatresistance, transparency, and curability and are suitable particularlyin molding (forming) of wafer-level lenses. Typically, in a knowntechnique, an organic-inorganic composite resin composition is used soas to give a cured product that has excellent heat resistance and lesssuffers from heat discoloration due to heating and deterioration inmechanical strength (see PTL 4). The organic-inorganic composite resincomposition includes an organic resin component (e.g., a cycloaliphaticepoxide) and an inorganic fine particle component. Although in a knowntransparent encapsulating material, a cycloaliphatic epoxide ispreferably used so as to give a cured product having a higher glasstransition temperature (see PTL 5).

Various attempts have been made to allow cured products of curablecompositions including a cycloaliphatic epoxide to have still higherglass transition temperatures and/or still higher mechanical strength.Typically, incorporation of a glycidyl-containing compound, anoxetanyl-containing compound, or a silicone compound into acycloaliphatic epoxide has been attempted. Typically, a known curablecomposition includes a silicone material, an organic compound, ahydrosilylation catalyst, and fine polymer particles (see PTL 1). Thesilicone material is a compound containing at least two SiH groups permolecule. The organic compound has a triallyl isocyanurate structure andcontains carbon-carbon double bonds that are reactive with the SiHgroups. A known thermosetting resin composition includes a polysiloxane,an aromatic ring-containing epoxy resin, and a curing agent (see PTL 2).The polysiloxane contains a reactive cyclic ether group and contains Dunits and T units in a random form. The D units are derived from adialkoxysilane containing an aromatic ring. The T units are derived froma trialkoxysilane containing a reactive cyclic ether group.Independently, a known optical resin composition includes asilsesquioxane derivative, an alicyclic skeleton-containing epoxy resin,and a curing agent and gives an optical component having an Abbe number55 of or more (see PTL 3). The silsesquioxane derivative has a randomstructure and/or a ladder-like structure (either one or both of a randomstructure and a ladder-like structure) and is obtained by hydrolyticallycondensing an alkyl- or aryl-containing trialkoxysilane with anepoxy-containing trialkoxysilane.

Independently, a disclosed method for producing an optical element suchas a lens includes producing an optical element wafer and cutting theoptical element wafer to give pieces of optical elements (see PTL 6). Inthe method, the optical element wafer is produced by a method thatincludes the step of pressing or stamping an optical element material toa predetermined thickness using an upper stamper mold and a lowerstamper mold. The optical element material is then cured by light orheat. Another disclosed method for forming an electronic element moduleincludes forming an integrated assembly as a stack of two or moredifferent optical element array plates (see PTL 7). The assembly is thencut at once to give chip sections to thereby give the electronic elementmodule including a stack of two or more lenses. Each of the opticalelement array sheets includes two or more lenses arrayed in a matrix.

All the citations, however, fail to disclose a way to allow a materialto maintain its high curability and to still give a cured product havinghigher mechanical strength and still having a high glass transitiontemperature as maintained. In addition, all the citations fail todescribe a way to efficiently give a high-quality wafer-level lens asmentioned above.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication (JP-A) No.2011-1401

PTL 2: JP-A No. 2011-132416

PTL 3: JP-A No. 2012-116989

PTL 4: JP-A No. 2008-133439

PTL 5: JP-A No. 2008-189698

PTL 6: JP-A No. 2010-102312

PTL 7: JP-A No. 2010-173196

SUMMARY OF INVENTION Technical Problem

Accordingly, it is an object of the present invention to provide acurable composition that can be cured satisfactorily and can form acured product having a high glass transition temperature as maintainedand having high mechanical strength.

It is another object of the present invention to provide a cured productthat has a high glass transition temperature as maintained and still hashigh mechanical strength.

It is yet another object of the present invention to provide an opticalelement and an optical device each of which can be obtained withexcellent productivity and has heat resistance and mechanical strengthboth at high levels.

It is still another object of the present invention to provide a curablecomposition (curable composition for a wafer-level lens) that can becured satisfactorily and can form a wafer-level lens having excellentoptical properties, a high glass transition temperature as maintained,and high mechanical strength.

It is another object of the present invention to provide a wafer-levellens that can be produced with excellent productivity and has excellentoptical properties, a high glass transition temperature as maintained,and high mechanical strength.

It is yet another object of the present invention to provide an opticaldevice that can be produced with excellent productivity and includes awafer-level lens having heat resistance and mechanical strength both athigh levels.

Solution to Problem

After intensive investigations to achieve the objects, the presentinventors have found that a curable composition including a specificsiloxane, a specific epoxide, and a curing agent can be curedsatisfactorily; and that the curable composition can form a curedproduct having a high glass transition temperature as maintained andstill having high mechanical strength. The present inventors have alsofound that a curable composition including a specific epoxide can becured satisfactorily; that the curable composition can give awafer-level lens having a high glass transition temperature asmaintained and still having high mechanical strength; and that thecurable composition, when further containing a specific siloxane, canefficiently give a wafer-level lens with still higher quality. Thepresent invention has been made based on these findings.

Specifically, the present invention provides, in an aspect, a curablecomposition including a cycloaliphatic epoxide (A), a siloxane (B), anda curing agent (C). The siloxane (B) contains at least two epoxy groupsper molecule.

In the curable composition, the cycloaliphatic epoxide

(A) may include a compound represented by Formula (I):

where X is selected from a single bond and a linkage group.

In the curable composition, the siloxane (B) containing at least twoepoxy groups per molecule may contain a cycloaliphatic epoxy group as atleast one of the epoxy groups.

The curable composition may contain the cycloaliphatic epoxide (A) in acontent of from 5 to 60 percent by weight based on the total amount (100percent by weight) of the curable composition.

In the curable composition, the cycloaliphatic epoxide (A) may include3,4,3′,4′-diepoxybicyclohexyl.

The curable composition may further include a hydrogenated glycidylether epoxide.

The curable composition may serve as a composition for optical elementformation.

The present invention provides, in another aspect, a cured product ofthe curable composition.

The present invention provides, in still another aspect, an opticalelement including a cured product of the curable composition.

The present invention provides, in yet another aspect, an optical deviceincluding the optical element.

In another aspect, the present invention provides a curable compositionfor a wafer-level lens. The curable composition contains acycloaliphatic epoxide (A′) represented by Formula (I):

where X is selected from a single bond and a linkage group.

The curable composition for a wafer-level lens may further contain asiloxane (B) containing at least two epoxy groups per molecule.

In the curable composition for a wafer-level lens, the siloxane (B)containing at least two epoxy groups per molecule may contain acycloaliphatic epoxy group as at least one of the epoxy groups.

The curable composition for a wafer-level lens may contain thecycloaliphatic epoxide (A′) in a content of from 5 to 60 percent byweight based on the total amount (100 percent by weight) of the curablecomposition.

The curable composition for a wafer-level lens may include3,4,3′,4′-diepoxybicyclohexyl as the cycloaliphatic epoxide (A′).

The curable composition for a wafer-level lens may further include ahydrogenated glycidyl ether epoxide.

The present invention provides, in another aspect, a method forproducing a wafer-level lens. The method includes subjecting the curablecomposition for a wafer-level lens to cast molding or injection molding.

In the method for producing a wafer-level lens, the cast molding mayinclude steps 1a, 2a, and 3a as follows. The step 1a is the step ofpreparing a wafer-level-lens mold including at least one lens pattern.The step 2a is the step of bringing the curable composition for awafer-level lens into contact with the wafer-level-lens mold. The step3a is the step of applying heat and/or light to the curable compositionfor a wafer-level lens to cure the curable composition to thereby give acured product of the curable composition.

In the method for producing a wafer-level lens, the cast molding mayfurther include the step 4a of annealing the cured product of thecurable composition for a wafer-level lens.

In the method for producing a wafer-level lens, the cast molding mayfurther include the step 5a of cutting the cured product of the curablecomposition for a wafer-level lens.

In the method for producing a wafer-level lens, the injection moldingmay include steps 1b, 2b, and 3b as follows. The step 1b is the step ofpreparing a wafer-level-lens mold including at least one lens pattern.The step 2b is the step of injecting the curable composition for awafer-level lens into the wafer-level-lens mold. The step 3b is the stepof applying heat and/or light to the curable composition for awafer-level lens to cure the curable composition to thereby give a curedproduct of the curable composition.

In the method for producing a wafer-level lens, the injection moldingmay further include the step 4b of annealing the cured product of thecurable composition for a wafer-level lens.

In yet another aspect, the present invention provides a wafer-level-lenssheet obtained by the method for producing a wafer-level lens.

In still another aspect, the present invention provides a wafer-levellens obtained by the method for producing a wafer-level lens.

The present invention provides, in another aspect, an optical deviceincluding the wafer-level lens.

The present invention provides, in still another aspect, a wafer-levellens stack including a stack of wafer-level lenses. The wafer-levellenses constituting the stack include a wafer-level lens obtained bycuring and molding the curable composition for a wafer-level lens.

The present invention provides, in yet another aspect, a method forproducing a wafer-level lens stack so as to produce the above-mentionedwafer-level lens stack. The method includes steps 1c, 2c, 3c, 4c, and 5cas follows. The step 1c is the step of preparing a wafer-level-lens moldincluding at least one lens pattern. The step 2c is the step of bringingthe curable composition for a wafer-level lens into contact with thewafer-level-lens mold. The step 3c is the step of applying heat and/orlight to the curable composition for a wafer-level lens to cure thecurable composition to thereby give a wafer-level-lens sheet. The step4c is the step of stacking a plurality of wafer-level-lens sheetsincluding the prepared wafer-level-lens sheet to give a wafer-level-lenssheet stack. The step 5c is the step of cutting the wafer-level-lenssheet stack.

The method for producing a wafer-level lens stack may further include astep 6c between the step 3c and the step 4c. The step 6c is the step ofannealing the wafer-level-lens sheet.

The present invention provides, in another aspect, a wafer-level-lenssheet stack as a stack of a plurality of wafer-level-lens sheetsincluding the wafer-level-lens sheet.

In addition and advantageously, the present invention provides anoptical device including the wafer-level lens stack.

Advantageous Effects of Invention

The curable composition according to the present invention, as havingthe configuration, can be cured satisfactorily and still can give acured product that has a high glass transition temperature as maintainedand exhibits high mechanical strength. The cured product excels inproperties such as heat resistance, transparency, and water-vaporresistance. The curable composition is therefore preferably usable as acomposition for optical element formation. The term “composition foroptical element formation” refers to a material for the formation of avariety of optical elements and optical devices.

The curable composition for a wafer-level lens according to the presentinvention, as having the configuration, can be cured satisfactorily andstill can form a wafer-level lens that has a high glass transitiontemperature as maintained and exhibits high mechanical strength. In apreferred embodiment, the curable composition for a wafer-level lensaccording to the present invention further contains a siloxanecontaining at least two epoxy groups per molecule. This curablecomposition can efficiently give a wafer-level lens with still higherquality. The curable composition for a wafer-level lens according to thepresent invention can significantly contribute to a smaller size, alighter weight, and higher performance of an electronic productincluding the wafer-level lens.

As used herein the term “wafer-level lens” refers to a lens for use inthe wafer-level production of a camera to be used typically in a mobilephone. The “wafer-level lens” may have a size in diameter of typicallyfrom about 1 to about 10 mm, and preferably from about 3 to about 5 mmand a thickness of typically from about 100 to about 1500 μm, andpreferably from about 500 to about 800 μm.

DESCRIPTION OF EMBODIMENTS

Curable Compositions

The curable composition according to the present invention is acomposition including a cycloaliphatic epoxide (A) as an essentialcomponent. In particular, preferred embodiments of the curablecomposition according to the present invention include two embodiments(first and second embodiments) as follows. The curable compositionsaccording to the present invention, in these embodiments, moreefficiently exhibit the advantageous effects of the present invention.

The curable composition according to the first embodiment of the presentinvention is a curable composition that includes a cycloaliphaticepoxide (A), a siloxane (B), and a curing agent (C) as essentialcomponents. As used herein the term “siloxane (B)” refers to a siloxanethat contains at least two epoxy groups per molecule (in one molecule).The curable composition according to the first embodiment is alsoreferred to as a “curable composition [1]according to the presentinvention”.

The curable composition according to the second embodiment of thepresent invention is a curable composition for a wafer-level lens. Thiscurable composition includes a cycloaliphatic epoxide (A′) representedby Formula (I) below as an essential component. The curable compositionaccording to the second embodiment is also referred to as a “curablecomposition [2] according to the present invention”

Curable Composition [1] According to Present Invention

The curable composition [1] according to the present invention is acomposition including the cycloaliphatic epoxide (A), the siloxane (B),and the curing agent (C) as essential components, as described above.The curable composition [1] according to the present invention mayfurther include one or more other components in addition to the abovecomponents.

Cycloaliphatic Epoxide (A)

The cycloaliphatic epoxide (A) acts as an essential component of thecurable composition [1] according to the present invention and is acompound containing at least a cycloaliphatic (alicyclic) structure andan epoxy group in molecule. Specifically, the cycloaliphatic epoxide (A)is exemplified by compounds (i) and compounds (ii). The compounds (i)each contain an epoxy group (cycloaliphatic epoxy group) including anoxygen atom and two adjacent carbon atoms constituting an alicycle. Thecompounds (ii) each contain an epoxy group directly bonded to analicycle through a single bond. The cycloaliphatic epoxides (A) do notinclude the siloxanes (B) and the after-mentioned hydrogenated glycidylether epoxides.

The compounds (i) for use herein may optionally be selected from amongknown or common ones, where the compounds (i) contain an epoxy group(cycloaliphatic epoxy group) including an oxygen atom and two adjacentcarbon atoms constituting an alicycle. In particular, the cycloaliphaticepoxy group is preferably a cyclohexene oxide group.

Of the compounds (i) containing an epoxy group (cycloaliphatic epoxygroup) including an oxygen atom and two adjacent carbon atomsconstituting an alicycle, preferred are cyclohexene oxide-containingcompounds, of which particularly preferred is a compound represented byFormula (I) (cycloaliphatic epoxide). These are preferred from theviewpoints of transparency and heat resistance of the cured product. Thecompound represented by Formula (I) is also referred to as a“cycloaliphatic epoxide (A′)”. Formula (I) is expressed as follows:

In Formula (I), X is selected from a single bond and a linkage group.The linkage group refers to a divalent group containing at least oneatom and is exemplified by divalent hydrocarbon groups, carbonyl, etherbond, ester bond, carbonate, amido, and groups each including two ormore of them linked to each other.

The cycloaliphatic epoxide (A) of Formula (I) in which X is a singlebond includes 3,4,3′,4′-diepoxybicyclohexyl.

The divalent hydrocarbon groups are exemplified by linear orbranched-chain C₁-C₁₈ alkylene, and divalent alicyclic hydrocarbongroups. The linear or branched-chain C₁-C₁₈ alkylene is exemplified bymethylene, methylmethylene, dimethylmethylene, ethylene, propylene, andtrimethylene. The divalent alicyclic hydrocarbon groups are exemplifiedby divalent cycloalkylene (including cycloalkylidene), such as1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene,1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, andcyclohexylidene.

The linkage group X is preferably any of oxygen-containing linkagegroups such as —CO—, —O—CO—O—, —COO—, —O—, and —CONH—; groups eachincluding two or more of them linked to each other; and groups eachincluding one or more of these groups and one or more divalenthydrocarbon groups linked to each other. The divalent hydrocarbon groupsare as exemplified above.

The cycloaliphatic epoxide represented by Formula (I) is typified bycompounds represented by Formulae (I-1) to (I-10) below. In Formulae(I-5) and (I-7), l and m each represent an integer of from 1 to 30. InFormula (I-5), R represents C₁-C₈ alkylene and is exemplified by linearor branched-chain alkylene such as methylene, ethylene, propylene,isopropylene, butylene, isobutylene, s-butylene, pentylene, hexylene,heptylene, and octylene. Among them, preferred is C₁-C₃ linear orbranched-chain alkylene such as methylene, ethylene, propylene, andisopropylene. In Formulae (I-9) and (I-10), n1 to n6 each represent aninteger of from 1 to 30.

The compounds (ii) containing an epoxy group directly bonded to analicycle through a single bond are exemplified by compounds representedby Formula (II):

In Formula (II), R′ represents a group corresponding to a p-hydricalcohol, except for removing —OH in the number of p from the structuralformula of the alcohol. The numbers p and n represent, independently ineach occurrence, a natural number. The p-hydric alcohol [R′—(OH)_(p)] isexemplified by polyhydric alcohols (e.g., C₁-C₁₅ alcohols) such as2,2-bis(hydroxymethyl)-1-butanol. The number p is preferably from 1 to6, and the number n is preferably from 1 to 30. When p is 2 or more, twoor more occurrences of n in the group in the brackets (outer brackets)may be identical or different. Specifically, the compounds areexemplified by an 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of2,2-bis(hydroxymethyl)-1-butanol, or a product available under the tradename of EHPE3150 (from Daicel Corporation).

The curable composition [1] according to the present invention mayinclude, as the cycloaliphatic epoxide (A), each of different epoxidesalone or in combination. The cycloaliphatic epoxide (A) may be producedby a known or common method. The cycloaliphatic epoxide (A) for useherein may also be available as commercial products typically under thetrade names of CELLOXIDE 2021P and CELLOXIDE 2081 (each from DaicelCorporation).

As the cycloaliphatic epoxide (A), preferred are the compoundrepresented by Formula (I-1)[3,4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate or theproduct available under trade name of CELLOXIDE 2021P (from DaicelCorporation)]; and 3,4,3′,4′-diepoxybicyclohexyl. In particular, thecurable composition preferably includes 3,4,3′,4′-diepoxybicyclohexyl asan essential component. This is preferred from the viewpoints of thecurability of the curable composition, and the water-vapor resistance,heat resistance (glass transition temperature), low shrinkage, and lowlinear expansion of the cured product.

The curable composition [1] according to the present invention maycontain the cycloaliphatic epoxide (A) in a content (blending quantity)not critical, but preferably from 5 to 60 percent by weight, morepreferably from 10 to 55 percent by weight, and furthermore preferablyfrom 15 to 50 percent by weight, based on the total amount (100 percentby weight) of the curable composition. The curable composition, ifcontaining the cycloaliphatic epoxide (A) in a content out of the range,may cause the cured product to hardly have heat resistance andmechanical strength in a good balance at high levels.

In an embodiment, the curable composition [1] according to the presentinvention includes 3,4,3′,4′-diepoxybicyclohexyl as the cycloaliphaticepoxide (A). In this embodiment, the curable composition may contain the3,4,3′,4′-diepoxybicyclohexyl in an amount (blending quantity) notcritical, but preferably from 10 to 50 percent by weight, morepreferably from 15 to 45 percent by weight, and furthermore preferablyfrom 20 to 40 percent by weight, based on the total amount (100 percentby weight) of curable compounds contained in the curable composition.The curable composition, if containing 3,4,3′,4′-diepoxybicyclohexyl inan amount of less than 10 percent by weight, may exhibit insufficientcurability and/or may cause the cured product to be insufficient inwater-vapor resistance, heat resistance (glass transition temperature),low shrinkage, and/or low linear expansion in some use situations. Incontrast, the curable composition, if containing3,4,3′,4′-diepoxybicyclohexyl in an amount of greater than 50 percent byweight, may cause the cured product to have insufficient mechanicalstrength.

Siloxane (B)

The siloxane (B) acts as an essential component of the curablecomposition [1] according to the present invention and is a compoundthat contains at least two epoxy groups per molecule and includes asiloxane skeleton including a siloxane bond (Si—O—Si). The siloxaneskeleton in the siloxane (B) is exemplified by, but not limited to,cyclic siloxane skeletons; and polysiloxane skeletons typically oflinear or branched-chain silicones (straight chain or branched chainpolysiloxanes) and of cage-like or ladder-like polysilsesquioxanes. Ofthe siloxane skeletons, preferred are cyclic siloxane skeletons. Theseare preferred from the viewpoints of the curability of the curablecomposition, and the heat resistance and mechanical strength of thecured product. Specifically, cyclic siloxanes containing at least twoepoxy groups per molecule are preferred as the siloxane (B).

In an embodiment, the siloxane (B) includes a cyclic siloxane containingat least two epoxy groups. In this embodiment, the siloxane ring mayinclude Si—O units in a number not critical, but preferably from 2 to12, and more preferably from 4 to 8. This is preferred from theviewpoints of the curability of the curable composition, and the heatresistance and mechanical strength of the cured product. The number ofthe Si—O units is equal to the number of silicon atoms constituting thesiloxane ring.

The siloxane (B) may include epoxy groups in a number not critical, aslong as being 2 or more, but preferably from 2 to 4, and more preferably3 or 4. This is preferred from the viewpoints of the curability of thecurable composition, and the heat resistance and mechanical strength ofthe cured product.

The siloxane (B) may have an epoxy equivalent not critical, butpreferably from 180 to 400, more preferably from 240 to 400, andfurthermore preferably from 240 to 350. This is preferred from theviewpoints of the curability of the curable composition, and the heatresistance and mechanical strength of the cured product. The epoxyequivalent is determined in conformity with JIS K7236.

Though not limited, at least one (preferably at least two, and morepreferably all) of the epoxy groups in the siloxane (B) is preferably acycloaliphatic epoxy group. The “cycloaliphatic epoxy group” refers toan epoxy group including an oxygen atom and two adjacent carbon atomsconstituting an alicycle. In particular, at least one (preferably atleast two, and more preferably all) of the epoxy groups is preferably acyclohexene oxide group. The “cyclohexene oxide group” refers to anepoxy group including an oxygen atom and two adjacent carbon atomsconstituting a cyclohexane ring. These are preferred from the viewpointof the curability of the curable composition.

The siloxane (B) is exemplified by a compound (cyclic siloxane)represented by Formula (1):

In Formula (1), R¹ and R² are, independently in each occurrence,selected from alkyl and a monovalent group containing a cycloaliphaticepoxy group, where at least two occurrences of R¹ and R² in the compoundrepresented by Formula (1) are each independently a monovalent groupcontaining a cycloaliphatic epoxy group. In Formula (1), q represents aninteger of 3 or more and is preferably an integer of from 3 to 6. R¹ andR² in each occurrence in the compound represented by Formula (1) may beidentical or different. The plural occurrences of R¹ may be identical ordifferent. Likewise, the plural occurrences of R² may be identical ordifferent.

The monovalent group containing a cycloaliphatic epoxy group isexemplified by, but not limited to, a group represented by -A-R³, whereA represents alkylene, and R³ represents a cycloaliphatic epoxy group.The alkylene A is exemplified by C₁-C₁₈ linear or branched-chainalkylene such as methylene, methylmethylene, dimethylmethylene,ethylene, propylene, and trimethylene. The group R³ is exemplified bycyclohexene oxide group.

More specifically, the siloxane (B) is exemplified by2,4-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,6,8,8-hexamethyl-cyclotetrasiloxane,4,8-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,2,4,6,6,8-hexamethyl-cyclotetrasiloxane,2,4-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-6,8-dipropyl-2,4,6,8-tetramethyl-cyclotetrasiloxane,4,8-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,6-dipropyl-2,4,6,8-tetramethyl-cyclotetrasiloxane,2,4,8-tri[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,6,8-pentamethyl-cyclotetrasiloxane,2,4,8-tri[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-6-propyl-2,4,6,8-tetramethyl-cyclotetrasiloxane,2,4,6,8-tetra[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,8-tetramethyl-cyclotetrasiloxane,and epoxy-containing silsesquioxanes. Furthermore specifically, thesiloxane (B) is exemplified by cyclic siloxanes containing at least twoepoxy groups per molecule and being represented by the formulae:

Examples of the siloxane (B) for use herein also include silicone resinscontaining cycloaliphatic epoxy groups, described in JP-A No.2008-248169; and organopolysilsesquioxane resins containing at least twoepoxy functional groups per molecule, described in JP-A No. 2008-19422.

The curable composition [1] according to the present invention mayinclude, as the siloxane (B), each of different siloxanes alone or incombination. The siloxane (B) for use herein is also available ascommercial products typically under the trade names of X-40-2678,X-40-2670, and X-40-2720 (each from Shin-Etsu Chemical Co., Ltd.).

The curable composition [1] according to the present invention maycontain the siloxane (B) in a content (blending quantity) not critical,but preferably from 1 to 50 percent by weight, more preferably from 5 to45 percent by weight, and furthermore preferably from 10 to 40 percentby weight, based on the total amount (100 percent by weight) of thecurable composition [1] according to the present invention. The curablecomposition, if containing the siloxane (B) in a content out of therange, may hardly allow the cured product to have heat resistance andmechanical strength in a good balance at high levels.

The curable composition [1] according to the present invention maycontain the siloxane (B) in an amount (blending quantity) not critical,but preferably from 1 to 60 percent by weight, more preferably from 5 to55 percent by weight, and furthermore preferably from 10 to 50 percentby weight, based on the total amount (100 percent by weight) of curablecompounds contained in the curable composition. The total amount hereinis the total amount of curable compounds such as epoxides and oxetanecompounds. The curable composition, if containing the siloxane (B) in anamount out of the range, may hardly allow the cured product to have heatresistance and mechanical strength in a good balance at high levels.

Curing Agent (C)

The curing agent (C) acts as an essential component of the curablecomposition [1] according to the present invention. The curing agent (C)is a compound that functionally initiates or promotes the curingreaction of a curable compound (in particular, an epoxide) or reactswith the curable compound to cure the curable composition. The curablecompound contains a curable group (in particular, an epoxy group) and isexemplified by the cycloaliphatic epoxide (A) and the siloxane (B). Thecuring agent (C) is exemplified by known or common curing agents such ascuring catalysts. The curable composition [1] according to the presentinvention may include each of different curing agents alone or incombination as the curing agent (C).

In an embodiment, a curing catalyst is used as the curing agent (C). Thecuring catalyst for use herein is exemplified by, but not limited to,cationic catalysts (cationic-polymerization initiators). The cationiccatalysts generate a cationic species upon the application of light (inparticular, an ultraviolet ray) or heat to initiate polymerization.Specifically, the curing catalyst is exemplified by photo-cationicpolymerization initiators (photoacid generators) and thermal-cationicpolymerization initiators (thermal acid generators). In an embodiment,the curing agent (C) is a curing catalyst acting as a photo-cationicpolymerization initiator or thermal cationic polymerization initiator.In this embodiment, the resulting curable composition may readilyexhibit excellent curability to efficiently give a cured product withsmaller tack. In contrast, typically assume that the curable compositionemploys, as the curing agent (C), an acid anhydride well known as acuring agent for epoxy resins. In this case, the curable composition mayreadily have remarkably inferior curability, and this may impede theproduction of a cured product with high productivity.

The cationic catalysts that generate a cationic species upon theapplication of light (in particular, an ultraviolet ray) are alsoreferred to as photo-cationic polymerization initiators and areexemplified by hexafluoroantimonate salts, pentafluorohydroxy antimonatesalts, hexafluorophosphate salts, and hexafluoroarsenate salts. Thecationic catalysts (photo-cationic polymerization initiators) may alsobe preferably selected from commercial products available typicallyunder the trade names of: UVACURE 1590 (from DAICEL-CYTEC Company,Ltd.); CD-1010, CD-1011, and CD-1012 (each from Sartomer Company Inc.,U.S.A.); IRGACURE 264 (from BASF SE); CIT-1682 (from Nippon Soda Co.,Ltd.); and CPI-101A (from San-Apro Ltd.).

The cationic catalysts that generate a cationic species upon theapplication of heat (heat treatment) are also referred to as thermalcationic polymerization initiators and are exemplified by aryldiazoniumsalts, aryliodonium salts, arylsulfonium salts, and arene-ion complexes.The thermal cationic polymerization initiators for use herein are alsopreferably selected from commercial products available typically underthe trade names of: PP-33, CP-66, and CP-77 (each from ADEKACORPORATION); FC-509 (from 3M Company); UVE1014 (from G.E.); San-AidSI-60L, San-Aid SI-80L, San-Aid SI-100L, San-Aid SI-110L, and San-AidSI-150L (each from SANSHIN CHEMICAL INDUSTRY CO., LTD.); and CG-24-61(from Ciba Japan K.K.). The thermal cationic polymerization initiatorsmay also be selected from compounds between a chelate compound and asilanol; and compounds between the chelate compound and a phenol. Thechelate compound is exemplified by a chelate compound of a metal (e.g.,aluminum or titanium) with acetoacetic acid or a diketone. The silanolis exemplified by triphenylsilanol. The phenol is exemplified bybisphenol-S.

In an embodiment, the curing catalyst is used as the curing agent (C).In this embodiment, the curable composition [1] according to the presentinvention may contain the curing catalyst in an amount (blendingquantity) not critical, but preferably from 0.01 to 15 parts by weight,more preferably from 0.01 to 10 parts by weight, furthermore preferablyfrom 0.05 to 10 parts by weight, and particularly preferably from 0.1 to5 parts by weight, per 100 parts by weight of the total amount ofcurable compounds contained in the curable composition. The curablecomposition in this embodiment, when containing the curing catalyst inan amount within the range, can allow the cured product to excel in heatresistance, light resistance (lightfastness), and transparency.

Other Cationically Curable Compounds

The curable composition [1] according to the present invention mayfurther include one or more other cationically curable compounds. Theother cationically curable compounds are those other than the siloxane(B) and the cycloaliphatic epoxide (A) and hereinafter also simplyreferred to as “other cationically curable compounds”. The othercationically curable compounds are exemplified by epoxides other thanthe siloxane (B) and the cycloaliphatic epoxide (A); oxetane compounds;and vinyl ether compounds. Such other epoxides than the siloxane (B) andthe cycloaliphatic epoxide (A) are also referred to as “other epoxides”.In an embodiment, the curable composition contains one or more othercationically curable compounds. The curable composition in thisembodiment may have a controlled viscosity to be handled moresatisfactorily, and/or may become resistant to cure shrinkage upon theformation of a cured product. The curable composition [1] according tothe present invention may include each of different other cationicallycurable compounds alone or in combination.

The other epoxides are exemplified by aromatic glycidyl ether epoxidessuch as bisphenol-A epoxides, bisphenol-F epoxides, biphenol epoxides,phenol novolac epoxides, cresol novolac epoxides, bisphenol-A cresolnovolac epoxides, naphthalene epoxides, and epoxides derived fromtrisphenolmethane; aliphatic glycidyl ether epoxides such as aliphaticpolyglycidyl ethers; glycidyl ester epoxides; glycidylamine epoxides;and hydrogenated glycidyl ether epoxides (nuclear-hydrogenated aromaticglycidyl ether epoxides). Among them, hydrogenated glycidyl etherepoxides are preferred from the viewpoints of the transparency andwater-vapor resistance of the cured product. Specifically, thehydrogenated glycidyl ether epoxides are exemplified by hydrogenatedbisphenol-A epoxides such as2,2-bis[4-(2,3-epoxypropoxyl)cyclohexyl]propane,2,2-bis[3,5-dimethyl-4-(2,3-epoxypropoxyl)cyclohexyl]propane, andmultimers of them, where these compounds obtained by hydrogenation ofbisphenol-A epoxides; hydrogenated bisphenol-F epoxides such asbis[o,o-(2,3-epoxypropoxyl)cyclohexyl]methane,bis[o,p-(2,3-epoxypropoxyl)cyclohexyl]methane,bis[p,p-(2,3-epoxypropoxyl)cyclohexyl]methane,bis[3,5-dimethyl-4-(2,3-epoxypropoxyl)cyclohexyl]methane, and multimersof them, where these compounds are obtained by hydrogenation ofbisphenol-F epoxides; hydrogenated biphenol epoxides; hydrogenatedphenol novolac epoxides; hydrogenated cresol novolac epoxides;hydrogenated bisphenol-A cresol novolac epoxides; hydrogenatednaphthalene epoxides; and hydrogenated derivatives of epoxides derivedfrom trisphenolmethane.

The oxetane compounds are exemplified by trimethylene oxide,3,3-bis(vinyloxymethyl)oxetane, 3-ethyl-3-hydroxymethyloxetane,3-ethyl-3-(2-ethylhexyloxymethyl)oxetane,3-ethyl-3-(hydroxymethyl)oxetane, 3-ethyl-3-[(phenoxy)methyl]oxetane,3-ethyl-3-(hexyloxymethyl)oxetane, 3-ethyl-3-(chloromethyl)oxetane,3,3-bis(chloromethyl)oxetane,1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene,bis{[1-ethyl(3-oxetanyl)]methyl}ether,4,4′-bis[(3-ethyl-3-oxetanyl)methoxymethyl]bicyclohexyl,1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]cyclohexane, and3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane.

Among them, hydrogenated glycidyl ether epoxides and oxetane compoundsare preferred, of which hydrogenated glycidyl ether epoxides are morepreferred. These are preferred from the viewpoints of the transparency,water-vapor resistance, and mechanical strength of the cured product.

The other cationically curable compounds for use herein may also beselected from commercial products available typically under the tradenames of: YX8000 (from Mitsubishi Chemical Corporation); and ARONOXETANE OXT221 (from Toagosei Co., Ltd.).

The curable composition [1] according to the present invention maycontain the other cationically curable compound(s) in a content(blending quantity) not critical, but preferably from 0 to 50 percent byweight (e.g., 5 to 50 percent by weight), more preferably from 0 to 30percent by weight (e.g., 5 to 30 percent by weight), and furthermorepreferably from 0 to 15 percent by weight, based on the total amount(100 percent by weight) of the curable composition.

In an embodiment, the curable composition [1] according to the presentinvention includes one or more hydrogenated glycidyl ether epoxides. Inthis embodiment, the curable composition may include the hydrogenatedglycidyl ether epoxide(s) in an amount (blending quantity) not critical,but preferably from 5 to 40 percent by weight, and more preferably from10 to 30 percent by weight, based on the total amount (100 percent byweight) of curable compounds contained in the curable composition. Thecurable composition, when containing the hydrogenated glycidyl etherepoxide(s) in an amount of 5 percent by weight or more, may allow thecured product to have still higher mechanical strength. In contrast, thecurable composition, if containing the hydrogenated glycidyl etherepoxide(s) in an amount of greater than 40 percent by weight, may havepoor curability in some use situations.

In an embodiment, the curable composition [1] according to the presentinvention contains one or more oxetane compounds. In this embodiment,the curable composition may contain the oxetane compound(s) in an amount(blending quantity) not critical, but preferably from 5 to 30 percent byweight, and more preferably from 5 to 20 percent by weight, based on thetotal amount (100 percent by weight) of curable compounds contained inthe curable composition. The curable composition, when containing theoxetane compound(s) in an amount of 5 percent by weight or more, mayexhibit still better curability (in particular, curability upon curingby ultraviolet irradiation). In contrast, the curable composition, ifcontaining the oxetane compound(s) in an amount of greater than 30percent by weight, may cause the cured product to have poor heatresistance in some use situations.

Additives and Other Components

The curable composition [1] according to the present invention mayfurther include one or more other components such as additives. Theadditives include known or common additives and are exemplified by, butnot limited to, metal oxide particles, rubber particles, silicone- orfluorine-antifoaming agents, silane coupling agents, fillers,plasticizers, leveling agents, antistatic agents, mold-release agents(releasing agents), flame retardants, colorants, antioxidants,ultraviolet absorbers, ion adsorbents, and pigments. The curablecomposition [1]according to the present invention may contain suchadditive or additives each in a content (blending quantity) notcritical, but preferably 5 percent by weight or less based on the totalamount (100 percent by weight) of the curable composition. The curablecomposition [1] according to the present invention may include asolvent. However, the solvent, if present in an excessively highcontent, may cause the cured product to include bubbles. To preventthis, the content of the solvent is preferably controlled to 10 percentby weight or less, and more preferably 1 percent by weight or less,based on the total amount (100 percent by weight) of the curablecomposition [1] according to the present invention.

The curable composition [1] according to the present inventionpreferably excludes a composition containing a monoallyl diglycidylisocyanurate compound represented by Formula (2) below. The curablecomposition [1] according to the present invention, if including themonoallyl diglycidyl isocyanurate compound represented by Formula (2),may tend to be cured unsatisfactorily, and this may often impede thepreparation of a cured product without tack. In addition, this curablecomposition may readily cause disadvantages such as warping of theresulting cured product. In Formula (2), R⁴ and R⁵ are, independently ineach occurrence, selected from hydrogen and C₁-C₈ alkyl. The C₁-C₈ alkylis exemplified by linear or branched-chain alkyl such as methyl, ethyl,propyl, isopropyl, butyl, isobutyl, s-butyl, pentyl, hexyl, heptyl, andoctyl.

The curable composition [1] according to the present invention may beprepared by a process that is exemplified by, but not limited to, aprocess of formulating predetermined amounts of the cycloaliphaticepoxide (A), the siloxane (B), the curing agent (C), and other optionalcomponent(s) as needed, and stirring and mixing them. Where necessary,the stirring-mixing may be performed while removing bubbles typically invacuo. The stirring-mixing is performed at a temperature of typicallypreferably from about 10° C. to about 60° C. The stirring-mixing mayemploy a known or common apparatus such as planetary centrifugal mixers,single- or multi-screw extruders, planetary mixers, kneaders, anddissolvers.

The curable composition [1] according to the present invention, whencured, gives a cured product. This cured product is also referred to asa “cured product [1]according to the present invention”. The curing(curing reaction) of the curable composition [1] according to thepresent invention may be allowed to proceed by the application of heat(heat treatment) and/or light (light irradiation). The heat treatment,when employed, may be performed at a temperature not critical, butpreferably from 100° C. to 200° C., and more preferably from 120° C. to160° C. The temperature, however, may be adjusted as appropriatedepending typically on the types of the components and catalyst toundergo the reaction. The light irradiation, when employed, may beperformed using a light source. The light source is exemplified bymercury lamps, xenon lamps, carbon arc lamps, metal halide lamps,sunlight, electron beam sources, and laser sources. After the lightirradiation, heat treatment at a temperature typically from about 50° C.to about 180° C. may be performed so as to allow the curing reaction tofurther proceed.

The cured product [1] according to the present invention may have aninternal transmittance at 400 nm [for a thickness of 0.5 mm] notcritical, but preferably 70% or more (e.g., from 70% to 100%), morepreferably 75% or more, furthermore preferably 80% or more, andparticularly preferably 85% or more. The cured product [1] according tothe present invention may have a refractive index not critical, butpreferably from 1.40 to 1.60, and more preferably from 1.45 to 1.55. Thecured product [1] according to the present invention may have an Abbenumber not critical, but preferably 45 or more, and more preferably 50or more.

The cured product [1] according to the present invention may have aglass transition temperature (Tg) not critical, but preferably 100° C.or higher (e.g., from 100° C. to 200° C.), and more preferably 140° C.or higher. The cured product, if having a glass transition temperatureof lower than 100° C., may have insufficient heat resistance in some usesituations. The glass transition temperature of the cured product may bemeasured typically by any of measurement techniques such as a variety ofthermal analyses [e.g., DSC (differential scanning calorimeter) and TMA(thermomechanical analyzer)]; and dynamic viscoelastic measurement. Morespecifically, the glass transition temperature may be measured by ameasurement method described in working examples below.

The cured product [1] according to the present invention may have alinear expansion coefficient al not critical, but preferably from 40 to100 ppm/° C., and more preferably from 40 to 90 ppm/° C. The linearexpansion coefficient al is one at temperatures equal to or lower thanthe glass transition temperature. The cured product [1] according to thepresent invention may have a linear expansion coefficient α2 notcritical, but preferably from 90 to 150 ppm/° C., and more preferablyfrom 90 to 130 ppm/° C. The linear expansion coefficient α2 is one attemperatures equal to or higher than the glass transition temperature.The linear expansion coefficients α1 and α2 may be measured typically byTMA and, more specifically, may be measured by a measurement methoddescribed in the working examples.

The cured product [1] according to the present invention may have astorage elastic modulus at 25° C. not critical, but preferably 0.1 GPaor more, and more preferably 1 GPa or more. The storage elastic modulusof the cured product at 25° C. may be measured typically by the dynamicviscoelastic measurement, and, more specifically, may be measured by ameasurement method described in the working examples.

The cured product [1] according to the present invention may have abending strength (flexural strength) at 25° C. not critical, butpreferably from 80 to 200 MPa, and more preferably from 100 to 200 MPa.The cured product [1]according to the present invention may have abending strain at 25° C. not critical, but preferably 2% or more, andmore preferably 3% or more. The “bending strain” refers to a strain atthe maximum bending stress. The bending strength and bending strain ofthe cured product at 25° C. may be measured typically in conformity toJIS K7171 and, more specifically, may be measured by a measurementmethod described in the working examples.

The curable composition [1] according to the present invention can becured satisfactorily and still can form a cured product that has a highglass transition temperature as maintained and has high mechanicalstrength. The curable composition [1] is therefore preferably usableparticularly as a material for the formation of an optical element (as acomposition for optical element formation). Specifically, the opticalelement is an optical element including the cured product [1] obtainedby curing the curable composition [1] (composition for optical elementformation) according to the present invention. The optical element isexemplified by elements (members) that develop any of a variety ofoptical functions such as light diffusivity, optical transparency, andlight reflectivity; and components or members constituting opticaldevices. The term “optical device” as used herein generically refers todevices and equipment utilizing any of the optical functions.Specifically, the optical element is exemplified by elements in liquidcrystal display devices, such as color filters, color filter-protectingfilms, TFT planarizing films, substrate materials, light guide panels,prism sheets, polarizing plates (polarizing films), retarders(retardation films), viewing-angle compensation films,polarizer-protecting films, a variety of coating materials (coatingagents), adhesives (bonding agents), and end-sealing materials(end-sealing agents); elements in optical semiconductor display devices,such as molding compounds (molding agents) and encapsulants(encapsulating agents) for optical semiconductor elements, shield-glassprotecting films, shield-glass substitute materials, a variety ofcoating materials (coating agents), and adhesives (bonding agents);elements in plasma display panels, such as antireflection films, opticalcompensation films, housing materials, shield-glass protecting films,shield-glass substitute materials, a variety of coating materials(coating agents), and adhesives (bonding agents); elements in plasmaaddress liquid crystal displays, such as substrate materials, lightguide panels, prism sheets, polarizing plates, retardation films,viewing-angle compensation films, polarizer-protecting films, a varietyof coating materials (coating agents), and adhesives (bonding agents);elements in organic electroluminescence displays, such as shield-glassprotecting films, shield-glass substitute materials, a variety ofcoating materials (coating agents), and adhesives (bonding agents); andelements in field emission displays, such as a variety of filmsubstrates, shield-glass protecting films, shield-glass substitutematerials, a variety of coating materials (coating agents), andadhesives (bonding agents).

In addition, the optical element is further exemplified by opticalelements used in the fields of optical recording, optical instruments,optical components, optical fibers, and optoelectronic functionalorganic materials. The optical elements for use in optical recording areexemplified by disc substrate materials for CD/CD-ROM, CD-R/RW,DVD-R/DVD-RAM, MO/MD, phase change discs (PDs), Blu-Ray, and opticalmemory cards; pick-up lenses; photo-detector units; protecting films; avariety of coating materials (coating agents), and adhesives (bondingagents). The optical elements for use in optical instruments areexemplified by elements for use in still cameras, such as lensmaterials, viewfinder prisms, target prisms, viewfinder covers,photo-detector units, a variety of coating materials (coating agents),and adhesives (bonding agents); elements for use in video cameras, suchas image-pickup lenses, viewfinders, a variety of coating materials(coating agents), and adhesives (bonding agents); elements for use inprojection television sets, such as projector lenses, protecting films,a variety of coating materials (coating agents), and adhesives (bondingagents); elements for use in optical sensing devices, such as lensmaterials, a variety of films, a variety of coating materials (coatingagents), and adhesives (bonding agents); and elements for use in camerasmounted to portable terminals (e.g., smartphones), such as lenses, avariety of coating materials (coating agents), and adhesives (bondingagents). The optical elements for use in optical components areexemplified by peripheral elements for optical switches in opticalcommunication systems, such as fiber materials, lenses, waveguides,elements (devices), a variety of coating materials (coating agents), andadhesives (bonding agents); peripheral elements for optical connectors,such as optical fiber materials, ferrules, a variety of coatingmaterials (coating agents), and adhesives (bonding agents); elements foruse in optical passive components or optical circuit components, such aslenses, waveguides, a variety of coating materials (coating agents), andadhesives (bonding agents); and peripheral elements for optoelectronicintegrated circuits (OEICs), such as substrate materials, fibermaterials, a variety of coating materials (coating agents), andadhesives (bonding agents). The optical elements for use in or foroptical fibers are exemplified by optical fibers, a variety of coatingmaterials (coating agents), and adhesives (bonding agents) each for usein decorative display illumination and light guides (light pipes),industrial-use sensors, indications and signs, and elements for thecoupling or connection of digital devices for communicationinfrastructures or for domestic use. The optical elements for use in orfor optoelectronic functional organic materials are exemplified byperipheral materials for organic EL devices, peripheral substratematerials for organic photorefractive elements, light amplifyingelements (light amplifiers) acting as light-light converting devices,optical computing elements, organic solar cells, and fiber materials,encapsulants (encapsulating agents) for such elements or devices, avariety of coating materials (coating agents), and adhesives (bondingagents).

The optical element is still further exemplified by optical elements foruse in the fields of automobiles and transportation equipment,architecture (building), and agriculture. The optical elements for usein automobiles and transportation equipment are exemplified by elementsfor use in automobiles, such as lamp materials, lamp reflectors, andlamp lenses for lamps such as headlamps, tail lamps (rear positionlamps), and body interior lamps, a variety of interior and and exteriortrims such as outer casings and interior panels, glass substitutes, avariety of coating materials (coating agents), and adhesives (bondingagents); elements for use in railroad vehicles, such as exterior parts,glass substitutes, a variety of coating materials (coating agents), andadhesives (bonding agents); and elements for use in aircraft, such asexterior parts, glass substitutes, a variety of coating materials(coating agents), and adhesives (bonding agents). The optical elementsfor use in architecture are exemplified by glass-interlayer films, glasssubstitutes, a variety of coating materials (coating agents), andadhesives (bonding agents). The optical elements for use in agricultureare exemplified by films for plastic greenhouses, a variety of coatingmaterials (coating agents), and adhesives (bonding agents).

The use of the optical element including the cured product [1] can givean optical device including the optical element, where the cured product[1] is obtained by curing the curable composition [1] (composition foroptical element formation) according to the present invention. Theoptical device is exemplified by, but not limited to, a variety ofoptical devices including any of the above-mentioned optical elements,such as liquid crystal display devices, optical semiconductor displaydevices, plasma display panels, organic electroluminescence displays,field emission displays, and portable terminals such as smartphones andmobile phones.

Curable Composition [2] According to Present Invention

The curable composition [2] according to the present invention is acurable composition for a wafer-level lens, where the curablecomposition includes a cycloaliphatic epoxide (A′) as an essentialcomponent, as described above. The curable composition [2] according tothe present invention preferably further includes a siloxane (B). Thecurable composition [2] according to the present invention is a curablecomposition suitable for the formation of a wafer-level lens. Thecurable composition [2] according to the present invention may furtherinclude one or more components other than those mentioned above.

Cycloaliphatic Epoxide (A′)

The cycloaliphatic epoxide (A′) acts as an essential component of thecurable composition [2] according to the present invention and is acompound represented by Formula (I). The cycloaliphatic epoxide (A′) isexemplified as with the cycloaliphatic epoxide (A′) described in thedescription of the curable composition [1] according to the presentinvention.

The curable composition [2] according to the present invention mayinclude, as the cycloaliphatic epoxide (A′), each of different epoxidesalone or in combination. The cycloaliphatic epoxide (A′) may be producedby a known or common method. The cycloaliphatic epoxide (A′) may also beselected from commercial products available typically under the tradenames of CELLOXIDE 2021P and CELLOXIDE 2081 (each from DaicelCorporation).

Among them, the cycloaliphatic epoxide (A′) is preferably selected fromthe compound represented by Formula (I-1)[3,4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate, or aproduct available under the trade name of CELLOXIDE 2021P (from DaicelCorporation) and 3,4,3′,4′-diepoxybicyclohexyl. In particular, thecurable composition for a wafer-level lens preferably includes4,3′,4′-diepoxybicyclohexyl as an essential component. This is preferredfrom the viewpoints of the curability of the curable composition, andthe water-vapor resistance, heat resistance (glass transitiontemperature), low shrinkage, and low linear expansion of the curedproduct and the wafer-level lens.

The curable composition [2] according to the present invention maycontain the cycloaliphatic epoxide (A′) in a content (blending quantity)not critical, but preferably from 5 to 60 percent by weight, morepreferably from 10 to 55 percent by weight, and furthermore preferablyfrom 15 to 50 percent by weight, based on the total amount (100 percentby weight) of the curable composition. The curable composition, ifcontaining the cycloaliphatic epoxide (A′) in a content out of therange, may hardly allow the cured product to have heat resistance andmechanical strength in a good balance at high levels.

In an embodiment, 3,4,3′,4′-diepoxybicyclohexyl is used as thecycloaliphatic epoxide (A′). In particular in this embodiment, thecurable composition [2] according to the present invention may containthe 3,4,3′,4′-diepoxybicyclohexyl in an amount (blending quantity) notcritical, but preferably from 10 to 50 percent by weight, morepreferably from 15 to 45 percent by weight, and furthermore preferablyfrom 20 to 40 percent by weight, based on the total amount (100 percentby weight) of curable compounds contained in the curable composition.The curable composition for a wafer-level lens, if containing3,4,3′,4′-diepoxybicyclohexyl in a content of less than 10 percent byweight, may be cured insufficiently and may cause the cured product andwafer-level lens to be insufficient in water-vapor resistance, heatresistance (glass transition temperature), low shrinkage, and/or lowlinear expansion in some use situations. In contrast, the curablecomposition, if containing 3,4,3′,4′-diepoxybicyclohexyl in a content ofgreater than 50 percent by weight, may cause the cured product andwafer-level lens to have insufficient mechanical strength.

Siloxane (B)

The curable composition [2] according to the present inventionpreferably further includes a siloxane (B). As used herein the term“siloxane (B)” refers to a siloxane that contains at least two epoxygroups per molecule. The curable composition, when including thesiloxane (B), can efficiently give a wafer-level lens having stillhigher quality. The siloxane (B) is exemplified as with the siloxane (B)described in the description of the curable composition [1] according tothe present invention.

The curable composition [2] according to the present invention mayinclude, as the siloxane (B), each of different siloxanes alone or incombination. The siloxane (B) for use herein may also be selected fromcommercial products available typically under the trade names ofX-40-2678, X-40-2670, and X-40-2720 (each from Shin-Etsu Chemical Co.,Ltd.).

The curable composition [2] according to the present invention maycontain the siloxane (B) in a content (blending quantity) not critical,but preferably from 1 to 50 percent by weight, more preferably from 5 to45 percent by weight, and furthermore preferably from 10 to 40 percentby weight, based on the total amount (100 percent by weight) of thecurable composition. The curable composition, if containing the siloxane(B) in a content out of the range, may hardly allow the wafer-level lensto have heat resistance and mechanical strength in a good balance athigh levels.

The curable composition [2] according to the present invention maycontain the siloxane (B) in an amount (blending quantity) not critical,but preferably from 1 to 60 percent by weight, more preferably from 5 to55 percent by weight, and furthermore preferably from 10 to 50 percentby weight, based on the total amount (100 percent by weight) of curablecompounds contained in the curable composition. The total amount hereinis, for example, the total amount of curable compounds such as epoxidesand oxetane compounds. The curable composition, if containing thesiloxane (B) in an amount out of the range, may hardly allow thewafer-level lens to have heat resistance and mechanical strength in agood balance at high levels.

Curing Agent (C)

The curable composition [2] according to the present invention mayfurther include a curing agent (C). The curing agent (C) is a compoundthat functionally initiates or promotes the curing reaction of a curablecompound (in particular, an epoxide), or reacts with the curablecompound to cure the curable composition for a wafer-level lens, wherethe curable compound contains a cationically curable functional group(in particular, an epoxy group) and is exemplified by the cycloaliphaticepoxide (A′) and the siloxane (B). The curing agent (C) is exemplifiedby known or common curing agents such as curing catalysts. The curablecomposition [2] according to the present invention may include, as thecuring agent (C), each of different curing agents alone or incombination.

In an embodiment, a curing catalyst is used as the curing agent (C). Thecuring catalyst for use herein is exemplified by, but not limited to,cationic catalysts (cationic-polymerization initiators). The cationiccatalysts generate a cationic species upon the application of light (inparticular, an ultraviolet ray) or heat to initiate polymerization.Specifically, the curing catalyst is exemplified by photo-cationicpolymerization initiators (photoacid generators) and thermal cationicpolymerization initiators (thermal acid generators). In an embodiment,the curing agent (C) is a curing catalyst acting as a photo-cationicpolymerization initiator or thermal cationic polymerization initiator.In this embodiment, the curable composition for a wafer-level lens mayreadily have excellent curability to efficiently give a cured productand a wafer-level lens each of which has smaller tack. In contrast,typically assume that the curable composition for a wafer-level lensemploys, as the curing agent (C), an acid anhydride well known as acuring agent for epoxy resins. In this case, the curable composition maytend to be cured remarkably unsatisfactorily and to hardly produce acured product and a wafer-level lens with high productivity.Specifically, the cationic catalyst is exemplified as with the cationiccatalyst described in the description of the curable composition [1]according to the present invention.

In an embodiment, the curable composition [2] according to the presentinvention may include the curing catalyst as the curing agent (C). Inthis embodiment, the curable composition may contain the curing catalystin an amount (blending quantity) not critical, but preferably from 0.01to 15 parts by weight, more preferably from 0.01 to 10 parts by weight,furthermore preferably from 0.05 to 10 parts by weight, and particularlypreferably from 0.1 to 5 parts by weight, per 100 parts by weight of thetotal amount of curable compounds contained in the curable composition.The curable composition, when using the curing catalyst in an amountwithin the range, can give a cured product and a wafer-level lens eachof which excels in heat resistance, light resistance (lightfastness),and transparency.

Other Cationically Curable Compound

The curable composition [2] according to the present invention mayfurther include one or more other cationically curable compounds. Theterm “other cationically curable compounds” hereinafter refers tocationically curable compounds other than the cycloaliphatic epoxide(A′) and the siloxane (B). The other cationically curable compounds areexemplified by other epoxides; oxetane compounds; and vinyl ethercompounds. The term “other epoxides” hereinafter refers to epoxidesother than the cycloaliphatic epoxide (A′) and the siloxane (B). Thecurable composition for a wafer-level lens, when containing the othercationically curable compound, may have a controlled viscosity to behandled more satisfactorily, and/or may become resistant to cureshrinkage upon the formation of a wafer-level lens. The curablecomposition [2] according to the present invention may include each ofdifferent other cationically curable compounds alone or in combination.

The other epoxides are exemplified by aromatic glycidyl ether epoxidessuch as bisphenol-A epoxides, bisphenol-F epoxides, biphenol epoxides,phenol novolac epoxides, cresol novolac epoxides, bisphenol-A cresolnovolac epoxides, naphthalene epoxides, and epoxides derived fromtrisphenolmethane; aliphatic glycidyl ether epoxides such as aliphaticpolyglycidyl ethers; glycidyl ester epoxides; glycidylamine epoxides;and cycloaliphatic epoxides excluding the cycloaliphatic epoxide (A′)and the siloxane (B), such as compounds containing an epoxy group bondedto an alicycle directly through a single bond, and hydrogenated glycidylether epoxides (e.g., nuclear-hydrogenated aromatic glycidyl etherepoxides). Specific examples of the other epoxides are as with the otherepoxides described in the description of the curable composition [1]according to the present invention.

Among them, oxetane compounds and hydrogenated glycidyl ether epoxidesare preferred, of which hydrogenated glycidyl ether epoxides are morepreferred. These are preferred from the viewpoints of the transparency,water-vapor resistance, and mechanical strength of the wafer-level lens.

The other cationically curable compounds for use herein may also beselected from commercial products available typically under the tradenames of: YX8000 (from Mitsubishi Chemical Corporation); and ARONOXETANE OXT221 (from Toagosei Co., Ltd.).

The curable composition [2] according to the present invention maycontain the other cationically curable compound(s) in a content(blending quantity) not critical, but preferably from 0 to 50 percent byweight (e.g., from 5 to 50 percent by weight), more preferably from 0 to30 percent by weight (e.g., 5 to 30 percent by weight), and furthermorepreferably from 0 to 15 percent by weight, based on the total amount(100 percent by weight) of the curable composition.

In an embodiment, the curable composition [2] according to the presentinvention includes a hydrogenated glycidyl ether epoxide. In thisembodiment, the curable composition may contain the hydrogenatedglycidyl ether epoxide in an amount (blending quantity) not critical,but preferably from 5 to 40 percent by weight, and more preferably from10 to 30 percent by weight, based on the total amount (100 percent byweight) of curable compounds contained in the curable composition. Thecurable composition, when containing the hydrogenated glycidyl etherepoxide in a content of 5 percent by weight or more, may allow thewafer-level lens to have still higher mechanical strength. In contrast,the curable composition for a wafer-level lens, if containing thehydrogenated glycidyl ether epoxide in a content of greater than 40percent by weight, may have poor curability in some use situations.

In an embodiment, the curable composition [2] according to the presentinvention includes an oxetane compound. In this embodiment, the curablecomposition may contain the oxetane compound in an amount (blendingquantity) not critical, but preferably from 5 to 30 percent by weight,and more preferably from 5 to 20 percent by weight, based on the totalamount (100 percent by weight) of curable compounds contained in thecurable composition. The curable composition for a wafer-level lens,when containing the oxetane compound in a content of 5 percent by weightor more, may be cured still more satisfactorily, particularly uponcuring by ultraviolet irradiation. In contrast, the curable compositionfor a wafer-level lens, if containing the oxetane compound in a contentof greater than 30 percent by weight, may cause poor heat resistance insome use situations.

Mold-release Agent

The curable composition [2] according to the present invention maycontain a mold-release agent. The curable composition, when containingthe mold-release agent, may tend to be readily released from awafer-level-lens mold. The mold-release agent is exemplified by, but notlimited to, known or common mold-release agents including fluorinecompounds (fluorine mold-release agents) such as fluorocarbon resins andfluoroalkyl-containing compounds; silicone compounds (siliconemold-release agents) such as silicone oils and silicone resins; waxessuch as polyethylene waxes and polypropylene waxes; long-chaincarboxylic acids; long-chain carboxylic acid metal salts; and polyhydricalcohols such as polyethylene glycols. Among them, preferred aremold-release agents containing at least one cationically curablefunctional group (e.g., epoxy group and/or oxetanyl group) per molecule.These mold-release agents are exemplified by fluorine compounds eachcontaining a cationically curable functional group; and siliconecompounds each containing a cationically curable functional group. Thecurable composition may include, as the mold-release agent, each ofdifferent agents alone or in combination. The mold-release agent for useherein may also be selected from commercial products available typicallyunder the trade name of E-1630 (from Daikin Industries Ltd.). Thecurable composition [2] according to the present invention may containthe mold-release agent in a content not critical, but preferably from0.1 to 10 percent by weight, and more preferably from 0.5 to 5 percentby weight, based on the total amount (100 percent by weight) of thecurable composition, although the content may be set as appropriatedepending typically on the type of the mold-release agent and moldingmethod.

Additives and Other Components

The curable composition [2] according to the present invention mayinclude one or more other components such as additives. The additivesare exemplified by, but not limited to, known or common additives suchas metal oxide particles, rubber particles, silicone- orfluorine-antifoaming agents, silane coupling agents, fillers,plasticizers, leveling agents, antistatic agents, flame retardants,colorants, antioxidants, ultraviolet absorbers, ion adsorbents, andpigments. The curable composition [2] according to the present inventionmay contain such additive or additives each in a content (blendingquantity) not critical, but preferably 5 percent by weight or less,based on the total amount (100 percent by weight) of the curablecomposition. The curable composition [2] according to the presentinvention may include a solvent. However, the solvent, if present in anexcessively high content, may cause the wafer-level lens to includebubbles. To prevent this, the content of the solvent is preferablycontrolled to 10 percent by weight or less, and more preferably 1percent by weight or less, based on the total amount (100 percent byweight) of the curable composition [2] according to the presentinvention.

The curable composition [2] according to the present inventionpreferably excludes a composition including the monoallyl diglycidylisocyanurate compound represented by Formula (2). The curablecomposition [2] according to the present invention, if including themonoallyl diglycidyl isocyanurate compound represented by Formula (2),may tend to be cured unsatisfactorily, and this may often impede thepreparation of a wafer-level lens without tack. In addition, thiscurable composition may readily cause disadvantages such as warping ofthe resulting wafer-level lens. The curable composition may also tend tohardly allow the resulting wafer-level lens to have eccentric precision(molding precision) at certain level.

The curable composition [2] according to the present invention may beprepared by a process that is exemplified by, but not limited to, aprocess of formulating predetermined amounts of the cycloaliphaticepoxide (A′), and, as needed, optional components such as the siloxane(B), the curing agent (C), and other components, and stirring and mixingthem. The stirring-mixing may be performed while removing bubblestypically in vacuo according to necessity. The stirring-mixing isperformed at a temperature of typically preferably from about 10° C. toabout 60° C. The stirring-mixing may employ a known or common apparatussuch as planetary centrifugal mixers, single- or multi-screw extruders,planetary mixers, kneaders, and dissolvers.

The curable composition [2] according to the present invention can becured satisfactorily and, when cured, can give a cured product that hasa high glass transition temperature as maintained and still has highmechanical strength. This cured product is hereinafter also referred toas “cured product [2] according to the present invention” The curing ofthe curable composition [2] according to the present invention may beallowed to proceed typically by a method described in the description ofthe method for producing a wafer-level lens mentioned below.

The cured product [2] according to the present invention may have aninternal transmittance at 400 nm [for a thickness of 0.5 mm] notcritical, but preferably 70% or more (e.g., from 70% to 100%), morepreferably 75% or more, furthermore preferably 80% or more, andparticularly preferably 85% or more. The cured product [2] according tothe present invention may have a refractive index not critical, butpreferably from 1.40 to 1.60, and more preferably from 1.45 to 1.55. Thecured product [2]according to the present invention may have an Abbenumber not critical, but preferably 45 or more, and more preferably 50or more.

The cured product [2] according to the present invention may have aglass transition temperature (Tg) not critical, but preferably 100° C.or higher (e.g., from 100° C. to 200° C.), and more preferably 140° C.or higher. The curable composition, if having a glass transitiontemperature of lower than 100° C., may cause the cured product to haveinsufficient heat resistance in some use situations. The glasstransition temperature of the cured product may be measured typically byany of techniques such as a variety of thermal analyses [e.g., DSC(differential scanning calorimeter) and TMA (thermomechanicalanalyzer)]; and dynamic viscoelastic measurement. More specifically, theglass transition temperature may be measured by the measurement methoddescribed in the working examples.

The cured product [2] according to the present invention may have alinear expansion coefficient (α1) not critical, but preferably from 40to 100 ppm/° C., and more preferably from 40 to 90 ppm/° C. The linearexpansion coefficient (α1) is one at temperatures equal to or lower thanthe glass transition temperature. The cured product [2] according to thepresent invention may have a linear expansion coefficient α2 notcritical, but preferably from 90 to 150 ppm/° C., and more preferablyfrom 90 to 130 ppm/° C. The linear expansion coefficient α2 is one attemperature equal to or higher than the glass transition temperature.The linear expansion coefficients α1 and α2 of the cured product may bemeasured typically by TMA and, more specifically, may be measured by themeasurement method described in the working examples.

The cured product [2] according to the present invention may have astorage elastic modulus at 25° C. not critical, but preferably 0.1 GPaor more, and more preferably 1 GPa or more. The storage elastic modulusof the cured product at 25° C. may be measured typically by dynamicviscoelastic measurement and, more specifically, may be measured by themeasurement method described in the working examples.

The cured product [2] according to the present invention may have abending strength at 25° C. not critical, but preferably from 80 to 200MPa, and more preferably from 100 to 200 MPa. The cured product [2]according to the present invention may have a bending strain at 25° C.not critical, but preferably 2% or more, and more preferably 3% or more.The bending strain refers to a train at the maximum bending stress. Thebending strength and bending strain of the cured product at 25° C. maybe measured typically in conformity with JIS K7171 and, morespecifically, may be measured by the measurement method described in theworking examples.

Method for Producing Wafer-level Lens

The curable composition [2] according to the present invention, whencured and molded, gives a wafer-level lens. The resulting wafer-levellens is hereinafter also referred to as a “wafer-level lens according tothe present invention”. Specifically, the wafer-level lens according tothe present invention may be obtained by a method for producing awafer-level lens according to the present invention. This methodincludes subjecting the curable composition [2] according to the presentinvention to cast molding or injection molding.

The molding of the wafer-level lens may employ a mold (wafer-level-lensmold). The mold may be made of any material that is exemplified by, butnot limited to, metals, glass, and plastics.

Cast Molding

A way to perform the cast molding is exemplified by a method includingsteps 1a, 2a, and 3a as follows.

The step 1a is the step of preparing a wafer-level-lens mold includingat least one lens pattern.

The step 2a is performed after the step 1a and is the step of bringingthe curable composition [2] according to the present invention intocontact with the wafer-level-lens mold.

The step 3a is performed after the step 2a and is the step of applyingheat (heat treatment) and/or light (light irradiation) to the curablecomposition [2] according to the present invention to cure the curablecomposition to thereby give a cured product of the curable composition.

The curing of the curable composition [2] according to the presentinvention is performed by the heat treatment and/or light irradiation(step 3a). The heat treatment, when employed, may be performed at atemperature not critical, but preferably from 100° C. to 200° C., andmore preferably from about 120° C. to about 160° C., although thetemperature may be adjusted as appropriate depending typically on thetypes of the components and catalyst to be subjected to the reaction.The light irradiation, when performed, may employ a light source. Thelight source for use herein is exemplified by mercury lamps, xenonlamps, carbon arc lamps, metal halide lamps, sunlight, electron beamsources, and laser sources. After the light irradiation, heat treatmentmay be performed typically at a temperature of from about 50° C. toabout 180° C. to allow the curing reaction to further proceed.

The cast molding may further include, after the step 3a, a step 4a asfollows.

The step 4a is the step of annealing the cured product (cured product[2]) of the curable composition [2] according to the present invention.

The annealing may be performed typically, but nonlimitatively by heatingat a temperature of from 100° C. to 200° C. for about 30 minutes toabout one hour. Before the annealing, the cured product may be demoldedfrom the wafer-level-lens mold, or not.

In an embodiment, the cast molding is performed by simultaneous moldingas mentioned below. In particular in this embodiment, the step 3a orstep 4a generally gives a wafer-level-lens sheet. The wafer-level-lenssheet refers to a cured product that is in the form of a sheet andincludes one or more wafer-level lenses formed adjacent to each other.In an embodiment, the wafer-level-lens sheet includes two or morewafer-level lenses. These wafer-level lenses may be arrayed regularly ormay be disposed randomly. The wafer-level-lens sheet, when cut and fromwhich an extra portion is removed, gives the wafer-level lens or lensesaccording to the present invention.

Specifically, in an embodiment, the cast molding is performed by thesimultaneous molding. In particularly in this embodiment, the castmolding may further include, after the step 3a or the step 4a, a step 5aas follows.

The step 5a is the step of cutting the cured product (the cured product[2], in general, the wafer-level-lens sheet) of the curable composition[2] according to the present invention.

The cutting of the cured product (the cured product [2]) of the curablecomposition [2] according to the present invention may be performedtypically by a known or common proceeding process.

More specifically, the way to perform the cast molding includes both thesimultaneous molding including steps 1-1, 1-2, and 1-3 as follows; andsingle-piece molding including steps 2-1 and 2-2 as follows.

Simultaneous Molding

The step 1-1 is the step of pouring or casting the curable composition[2] according to the present invention into a wafer-level-lens mold,where the mold includes two or more lens patterns arrayed in apredetermined direction in form; and applying heat and/or light to thecurable composition to cure the curable composition to give a curedproduct.

The step 1-2 is performed after the step 1-1 and is the step ofdemolding the cured product from the wafer-level-lens mold and annealingthe cured product to give a wafer-level-lens sheet as a cured productincluding two or more wafer-level lenses bound with each other.

The step 1-3 is performed after the step 1-2 and is the step of cuttingthe resulting cured product to give wafer-level lenses.

Single-piece Molding

The step 2-1 is the step of pouring or casting the curable composition[2] according to the present invention into a wafer-level-lens moldincluding one lens pattern; and applying heat and/or light to thecurable composition to cure the curable composition to thereby give acured product.

The step 2-2 is performed after the step 2-1 and is the step ofdemolding the cured product from the wafer-level-lens mold and annealingthe cured product to give a wafer-level lens.

Injection Molding

The injection molding is exemplified by a process including steps 1b,2b, and 3b, as follows.

The step 1b is the step of preparing a wafer-level-lens mold includingat least one lens pattern.

The step 2b is performed after the step 1b and is the step of injectingthe curable composition [2] according to the present invention into thewafer-level-lens mold.

The step 3b is performed after the step 2b and is the step of applyingheat and/or light to the curable composition [2] according to thepresent invention to cure the curable composition to thereby give acured product.

In the injection molding, the curable composition [2]according to thepresent invention is cured by the application of heat (heat treatment)and/or light (light irradiation). More specifically, the curablecomposition may be cured as in the curing in the cast molding.

The injection molding may further include, after the step 3b, a step 4bas follows.

The step 4b is the step of annealing the cured product (the curedproduct [2]) of the curable composition [2]according to the presentinvention.

The annealing may be performed typically, but nonlimitatively by heatingat a temperature of from 100° C. to 200° C. for about 30 minutes toabout one hour. Before the annealing, the cured product may be demoldedfrom the wafer-level-lens mold, or not.

The injection molding may further include, after the step 3b or the step4b, an additional step such as the step of removing burrs.

Assume that the curable composition [2] according to the presentinvention is subjected to the simultaneous molding in the cast molding.In this case, the curable composition preferably has a low viscosity andexhibits excellent fluidity (flowability). This is preferred because thecurable composition can be satisfactorily charged into thewafer-level-lens mold. The curable composition [2]according to thepresent invention, when subjected to the simultaneous molding, may havea viscosity at 25° C. not critical, but preferably 3600 mPa·s or less,more preferably 2500 mPa·s or less, furthermore preferably 2000 mPa·s orless, and particularly preferably 1500 mPa·s or less. The curablecomposition [2] according to the present invention, when having aviscosity controlled within the range, can have better fluidity, mayless cause bubbles to remain, and can be charged into thewafer-level-lens mold while inhibiting the injection pressure fromincreasing. Specifically, the curable composition [2] according to thepresent invention can be coated (applied) and charged moresatisfactorily and can contribute to better workability all through themolding operation of the curable composition.

The cured product (cured product [2]) of the curable composition [2]according to the present invention has excellent heat resistance even ina high-temperature environment at a temperature of from about 100° C. to200° C. and can satisfactorily retain its shape. For this reason, thecured product, even when annealed after being demolded from thewafer-level-lens mold, can efficiently produce a wafer-level lens havingexcellent positional precision of the lens center. The positionalprecision of the lens center may be such that the positional deviation(misregistration) of the lens center is preferably about ±2 μm or less,and more preferably about ±1 μm or less. In an embodiment, two or morewafer-level lenses obtained by the method for producing a wafer-levellens according to the present invention are stacked and bonded to give awafer-level lens stack. The wafer-level lens stack is a cemented lensthat includes pixels in an extremely large number and has excellentoptical properties.

The cured product (cured product [2]) of the curable composition [2]according to the present invention can satisfactorily retain its shapeeven in a high-temperature environment, as mentioned above. The curedproduct therefore does not suffer from displacement in lens pitch evenduring or after annealing. In the step 1-3 of the simultaneous molding,two or more cured products are stacked to give an assembly, the cuttingline or lines are determined based on the uppermost cured product, andthe assembly is cut. This allows two or more wafer-level lenses to beseparated from each other without failure and enables cost reduction andmore efficient operation.

The wafer-level lens according to the present invention is usable alsoas a constitutional element of a wafer-level lens stack. The“wafer-level lens stack” herein refers to an assembly of two or morewafer-level lenses as stacked. Specifically, the wafer-level lens stackaccording to the present invention is a wafer-level lens stack includingthe wafer-level lens according to the present invention as a wafer-levellens constituting the stack. The wafer-level lens stack according to thepresent invention may include, as wafer-level lenses, the wafer-levellenses according to the present invention alone, or one or more of thewafer-level lenses according to the present invention in combinationwith one or more other wafer-level lenses. The wafer-level lens stackaccording to the present invention may include wafer-level lenses in anumber not critical, but typically from 2 to 5, and particularly 2 or 3.

The wafer-level lens stack according to the present invention may beproduced by a known or common method not limited. Typically, thewafer-level lens stack may be produced by stacking two or morewafer-level lenses including at least one wafer-level lens according tothe present invention, or by stacking two or more wafer-level-lenssheets including at least one wafer-level-lens sheet obtained by thesimultaneous molding to give a wafer-level-lens sheet stack (assembly ofwafer-level-lens sheets) and cutting the wafer-level-lens sheets. In thewafer-level lens stack (or the wafer-level-lens sheet stack) accordingto the present invention, adjacent wafer-level lenses (or adjacentwafer-level-lens sheets) may be bonded by a known or common bondingprocess or tool, or not.

More specifically, the wafer-level lens stack according to the presentinvention may be produced typically by a method including steps 1c, 2c,3c, 4c, and 5c as follows.

The step 1c is the step of preparing a wafer-level-lens mold includingat least one lens pattern.

The step 2c is performed after the step 1c and is the step of bringingthe curable composition [2] according to the present invention intocontact with the wafer-level-lens mold.

The step 3c is performed after the step 2c and is the step of applyingheat and/or light to the curable composition [2] according to thepresent invention to cure the curable composition to thereby give awafer-level-lens sheet.

The step 4c is performed after the step 3c and is the step of stackingtwo or more wafer-level-lens sheets including the above-preparedwafer-level-lens sheet to give a wafer-level-lens sheet stack.

The step 5c is performed after the step 4c and is the step of cuttingthe wafer-level-lens sheet stack.

The method for producing a wafer-level lens stack may further include,between the step 3c and the step 4c, a step 6c as follows.

The step 6c is the step of annealing the wafer-level-lens sheet.

The wafer-level lens and wafer-level lens stack according to the presentinvention have excellent heat resistance and optical properties and cansatisfactorily retain their shapes and maintain excellent opticalproperties even upon exposure to a high-temperature environment. Thewafer-level lens and wafer-level lens stack are preferably usabletypically as image pickup lenses for cameras in a variety of opticaldevices; ophthalmic lenses; light-beam condenser lenses; and lightdiffusing lenses. The cameras are exemplified by car-mounted cameras,digital cameras, personal computer-use cameras, mobile phone-usecameras, and security cameras (surveillance cameras). The optical deviceincluding the wafer-level lens or wafer-level lens stack according tothe present invention has high quality.

The wafer-level lens and wafer-level lens stack according to the presentinvention, when mounted onto a circuit board, can be mounted by reflowsoldering. Assume that the wafer-level lens according to the presentinvention is mounted to a camera module. Further assume that the cameramodule is mounted onto a printed circuit board (PCB) substrate typicallyof a mobile phone. In this case, the camera module can be veryefficiently mounted directly onto the substrate by the same solderreflow process as with surface mounting of other electronic components.This enables extremely efficient production of an optical device.

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples (working examples) below. It should benoted, however, that the examples are by no means intended to limit thescope of the present invention.

Production Example 1

Production of Cycloaliphatic Epoxide

An aliquot (70 g (0.68 mol)) of 95 percent by weight sulfuric acid and55 g (0.36 mol) of 1,8-diazabicyclo[5.4.0]undecene-7 (DBU) were mixedwith stirring to give a dehydration catalyst.

In a 3-liter flask equipped with a stirrer, a thermometer, and adewatering tube and further equipped with a thermally-insulateddistilling piping, were placed 1000 g (5.05 mol) of hydrogenatedbiphenol (4,4′-dihydroxybicyclohexyl), 125 g (0.68 mol as sulfuric acid)of the above-prepared dehydration catalyst, and 1500 g of pseudocumene,followed by heating of the flask. Water formation was detected aroundthe time point when the internal temperature became higher than 115° C.The temperature was further raised up to the boiling point ofpseudocumene (an internal temperature of from 162° C. to 170° C.),followed by a dehydration reaction under normal atmospheric pressure.The by-produced water was distilled and discharged through thedewatering tube out of the system. The dehydration catalyst was liquidunder the reaction conditions and finely dispersed in the reactionmixture. After a lapse of 3 hours, an approximately stoichiometricamount (180 g) of water was distilled, and the reaction was completed.The reaction mixture after the completion of reaction was subjected todistilling off of pseudocumene and subsequently to distillation at aninternal temperature of from 137° C. to 140° C. and an internal pressureof 10 Torr (1.33 kPa) using an Oldershaw distillation column with tentrays, and yielded 731 g of bicyclohexyl-3,3′-diene. In a reactor, werecharged 243 g of the obtained bicyclohexyl-3,3′-diene and 730 g of ethylacetate. The resulting mixture was combined with 274 g of a 30 percentby weight peracetic acid solution in ethyl acetate (with a water contentof 0.41 percent by weight) added dropwise over about 3 hours. Thedropwise addition was performed while blowing nitrogen into the gasphase and while controlling the reaction system internal temperature tobe 37.5° C. After the completion of dropwise addition of the peraceticacid solution, the resulting mixture was aged at 40° C. for one hour,followed by reaction completion. The crude reaction mixture at thecompletion of reaction was further washed with water at 30° C., fromwhich low-boiling compounds were removed at 70° C. and 20 mmHg, andyielded 270 g of a cycloaliphatic epoxide. The resulting cycloaliphaticepoxide had an oxirane oxygen content of 15.0 percent by weight. Thecycloaliphatic epoxide was subjected to ¹H-NMR measurement to find thata peak at δ of around 4.5 to 5 ppm disappeared, where the peak isassigned to a double bond; and that a proton peak assigned to an epoxygroup was detected at δ of around 3.1 ppm. Thus, the cycloaliphaticepoxide was identified as 3,4,3′,4′-diepoxybicyclohexyl.

Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-7

Components given in Table 1 below were blended according to blendingformulations given in Table 1 (in part by weight), stirred and mixed atroom temperature using a planetary centrifugal mixer, and yieldeduniform and transparent curable compositions (cationically curablecompositions).

Examples 2-1 to 2-8 and Comparative Examples 2-1 to 2-7

Components given in Table 2 below were blended according to blendingformulations given in Table 2 (in part by weight), stirred and mixed atroom temperature using a planetary centrifugal mixer, and yieldeduniform and transparent curable compositions (cationically curablecompositions) for a wafer-level lens.

Next, the above-obtained curable compositions or curable compositionsfor a wafer-level lens were cured by a heating treatment method or an UVirradiation method as follows, and yielded cured products. Tables 1 and2 indicate which curing method was employed for curing of each curablecomposition. For Examples 1-1 to 1-8 and Comparative Examples 1-1 to1-7, a flat mold without lens pattern was used for the preparation ofthe cured products. In contrast, for Examples 2-1 to 2-8 and ComparativeExamples 2-1 to 2-7, a mold (wafer-level-lens mold) including sevenaspherical lens patterns at the center thereof was used for thepreparation of samples (cured products) for release properties and lenspositional deviation evaluation; and a flat mold without lens patternwas used for the preparation of samples (cured products) for otherevaluations.

Heating Treatment Method

Each of the sample curable compositions was cured and molded to athickness of 0.5 mm in a molding profile below using an imprint moldingmachine (trade name NANOIMPRINTER NM-0501, supplied by Meisho Kiko Co.),cooled down to 80° C., demolded, further heated and thereby annealed for30 minutes in an oven preheated at 160° C., and yielded cured products(five cured products for each curable composition).

The molding profile was such that the curable composition is applied tothe mold at 25° C., the press shaft position is adjusted so as to give apredetermined thickness, the mold is pressed, raised in temperature upto 150° C. at a rate of 20° C. per minute, and held at 150° C. for 5minutes.

UV Irradiation Method

Each of the sample curable compositions is cured and molded to athickness of 0.5 mm in a molding profile below using an imprint moldingmachine (trade name NANOIMPRINTER NM-0501, supplied by Meisho Kiko Co.),demolded, further heated and thereby annealed for 30 minutes in an ovenpreheated at 160° C., and yielded cured products (five cured productsfor each curable composition).

The molding profile was such that the sample curable composition isapplied to the mold at 25° C., the press shaft position is adjusted soas to give a predetermined thickness, the mold is pressed, and anultraviolet ray is applied at an irradiation intensity of from 10 to 50mW/cm and a cumulative dose of from 2500 to 5000 mJ/cm².

Independently, test specimens (cured products) for the measurement ofbending strength and bending strain below were prepared by the methodsdescribed in the heating treatment method and the UV irradiation method,except that each sample curable composition was cured and molded to athickness of 1 mm.

TABLE 1 Formulation of curable composition Ex. 1-1 Ex. 1-2 Ex. 1-3 Ex.1-4 Ex. 1-5 Ex. 1-6 Ex. 1-7 Ex. 1-8 Curable compound S-1 30 20 20 30 4020 20 — S-2 — — — — — — — 30 C-1 40 30 50 40 30 30 30 35 CELLOXIDE 2021P15 — — — — — — — YX8000 15 35 30 20 30 15 15 20 OXT221 — 15 — — — 15 1515 EHPE3150 — — — 10 — 20 20 — Thermal cationic SI60L 0.31 — 0.31 0.310.31 — — — polymerization initiator Photo-cationic CPI101A — 0.45 — — —0.45 0.45 0.45 polymerization initiator Antioxidant IRG1010 1 1 1 1 1 11 1 HP10 1 1 1 1 1 1 1 1 Curing method heat UV heat heat heat UV UV UVFormulation of Com. Com. Com. Com. Com. Com. Com. curable compositionEx. 1-1 Ex. 1-2 Ex. 1-3 Ex. 1-4 Ex. 1-5 Ex. 1-6 Ex. 1-7 Curable compoundS-1 — — — — — — — S-2 — — — — — — — C-1 10 30 — 30 — 40 30 CELLOXIDE2021P 50 15 50 20 70 25 25 YX8000 — 20 30 30 — — — OXT221 20 15 — — — 1515 EHPE3150 20 20 20 20 30 20 30 Thermal cationic SI60L 0.31 — 0.31 0.310.31 — — polymerization initiator Photo-cationic CPI101A — 0.45 — — —0.45 0.45 polymerization initiator Antioxidant IRG1010 1 1 1 1 1 1 1HP10 1 1 1 1 1 1 1 Curing method heat UV heat heat heat UV UV

TABLE 2 Formulation of curable composition for wafer-level lens Ex. 2-1Ex. 2-2 Ex. 2-3 Ex. 2-4 Ex. 2-5 Ex. 2-6 Ex. 2-7 Ex. 2-8 Curable compoundS-1 30 20 20 30 40 20 20 — S-2 — — — — — — — 30 C-1 40 30 50 40 30 30 3035 CELLOXIDE 2021P 15 — — — — — — — YX8000 15 35 30 20 30 15 15 20OXT221 — 15 — — — 15 15 15 EHPE3150 — — — 10 — 20 20 — Thermal cationicSI60L 0.31 — 0.31 0.31 0.31 — — — polymerization initiatorPhoto-cationic CPI101A — 0.45 — — — 0.45 0.45 0.45 polymerizationinitiator Antioxidant IRG1010 1 1 1 1 1 1 1 1 HP10 1 1 1 1 1 1 1 1Mold-release agent E-1630 3 3 3 3 3 3 3 3 Curing method heat UV heatheat heat UV UV UV Formulation of curable composition Com. Com. Com.Com. Com. Com. Com. for wafer-level lens Ex. 2-1 Ex. 2-2 Ex. 2-3 Ex. 24Ex. 2-5 Ex. 2-6 Ex. 2-7 Curable compound S-1 — — — — — — — S-2 — — — — —— — C-1 10 30 — 30 — 40 30 CELLOXIDE 2021P 50 15 50 20 70 25 25 YX8000 —20 30 30 — — — OXT221 20 15 — — — 15 15 EHPE3150 20 20 20 20 30 20 30Thermal cationic SI60L 0.31 — 0.31 0.31 0.31 — — polymerizationinitiator Photo-cationic CPI101A — 0.45 — — — 0.45 0.45 polymerizationinitiator Antioxidant IRG1010 1 1 1 1 1 1 1 HP10 1 1 1 1 1 1 1Mold-release agent E-1630 3 3 3 3 3 3 3 Curing method heat UV heat heatheat UV UV

The abbreviations used in Tables 1 and 2 will be described below.

Curable Compounds

S-1: Cyclic siloxane containing four cycloaliphatic epoxy groups permolecule (trade name X-40-2670, supplied by Shin-Etsu Chemical Co.,Ltd.);

S-2: Cyclic siloxane containing two cycloaliphatic epoxy groups permolecule (trade name X-40-2678, supplied by Shin-Etsu Chemical Co.,Ltd.);

C-1: Compound prepared in Production Example 1(3,4,3′,4′-diepoxybicyclohexyl);

CELLOXIDE 2021P: 3,4-Epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate (trade name CELLOXIDE 2021P, suppliedby Daicel Corporation);

YX8000: Non-ester hydrogenated bisphenol diglycidyl compound (trade nameYX8000, supplied by Mitsubishi Chemical Corporation);

OXT221: 3-Ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane (tradename ARON OXETANE OXT221, supplied by Toagosei Co., Ltd.); and

EHPE3150: 1,2-Epoxy-4-(2-oxiranyl)cyclohexane adduct of2,2-bis(hydroxymethyl)-1-butanol (trade name EHPE3150, supplied byDaicel Corporation)

Thermal Cationic Polymerization Initiator

SI60L: Aromatic sulfonium salt (trade name San-Aid SI-60L, supplied bySANSHIN CHEMICAL INDUSTRY CO., LTD.)

Photo-cationic Polymerization Initiator

CPI101A: Aromatic sulfonium salt (trade name CPI-101A, supplied bySan-Apro Ltd.)

Antioxidants

IRG1010: Pentaerythritoltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenol)propionate] (trade nameIRGANOX 1010, supplied by BASF SE); and

HP10: 2,2′-Methylenebis(4,6-di-t-butylphenyl)octyl phosphite (trade nameHP-10, supplied by ADEKA CORPORATION)

Mold-release Agent

E-1630: 3-Perfluorohexyl-1,2-epoxypropane (trade name E-1630, suppliedby Daikin Industries Ltd.)

The curable compositions for a wafer-level lens obtained in Examples 2-1to 2-8 and Comparative Examples 2-1 to 2-7 were cured and molded usingthe mold including seven aspherical lens patterns at the center thereofby the procedure described in the heating treatment method or the UVirradiation method to give cured products (molded articles). Moldability(release properties and lens positional deviation) upon this process wasevaluated.

Release Properties

A sample was molded by the procedure described in the heating treatmentmethod or the UV irradiation method and demolded. The release propertiesupon demolding were evaluated according to criteria as follows.

Good: No release failure (e.g., molded article cracking) occurred uponfive continuous molding procedures;

Fair: Release failure (e.g., molded article cracking) occurred in oneout of five continuous molding procedures; and

Poor: Release failure (e.g., molded article cracking) occurred in two ormore out of five continuous molding procedures.

Lens Positional Deviation

Cured products (molded articles) were obtained by the proceduredescribed in the heating treatment method or the UV irradiation method.The center positions of seven lenses on each cured product were measuredusing an image measurement system (trade name IM-6020, supplied byKeyence Corporation). Positional deviation amounts of the seven lenscenters from a mold design value were measured, and averaged.

The curable compositions and cured products of them obtained in theexamples and comparative examples were subjected to evaluations asfollows.

Warping after Annealing

The cured products obtained in the examples and comparative examplesusing the flat mold were visually observed immediately after production(immediately after annealing), and whether they underwent warping afterannealing was evaluated. Specifically, a sample found to suffer from nowarping is indicated as “absence” (without warping after annealing); anda sample found to suffer from warping is indicated as “presence” (withwarping after annealing).

Conversion after Primary Curing

Each of the curable compositions (those including the thermal cationicpolymerization initiator) obtained in the examples and comparativeexamples was heated under a temperature condition below in a nitrogenatmosphere using a differential scanning calorimeter (DSC) (trade nameQ2000, supplied by TA Instruments). In this process, the heat generatedby curing of the curable composition was measured and defined as a “heatgenerated by curing of curable composition”. Next, each of the curablecompositions (those including the thermal cationic polymerizationinitiator) obtained in the examples and comparative examples was curedby the heating treatment method excluding the annealing and yielded acured product (cured resin after primary curing; cured resin beforeannealing). The cured product was further heated under the temperaturecondition below. In this process, the heat generated by curing of thecured product was measured and defined as a “heat generated by curing ofcured resin after primary curing”. Based on these, a curing rate aftermolding (conversion after primary curing) was calculated according to aformula as follows.

Temperature Condition

The sample is held at 50° C. for 3 minutes, subsequently raised intemperature at a rate of 20° C. per minute, and held at 250° C. for 3minutes.

Computational Formula for Curing Rate after MoldingCuring rate (%) after molding=[1−(Heat generated by curing of curedresin after primary curing)/(Heat generated by curing of curablecomposition)]×100

Conversion after Secondary Curing

Each of the curable compositions (those including the thermal cationicpolymerization initiator) obtained in the examples and comparativeexamples was heated under a temperature condition below in a nitrogenatmosphere using a differential scanning calorimeter (DSC) (trade nameQ2000, supplied by TA Instruments). In this process, the heat generatedby curing of the curable composition was measured and defined as a “heatgenerated by curing of curable composition”. Next, the cured resin afterthe primary curing was further subjected to annealing at 160° C. for 30minutes and yielded a cured product (cured resin after secondary curing;cured resin after annealing). The cured product was further heated undera temperature condition below. In this process, the heat generated bycuring of the cured product was measured and defined as a “heatgenerated by curing of cured resin after secondary curing”. Based onthese, a curing rate after annealing (conversion after secondary curing)was calculated according to a formula as follows.

Temperature Condition

The sample is held at 50° C. for 3 minutes, subsequently raised intemperature at a rate of 20° C. per minute, and held at 250° C. for 3minutes.

Computational Formula for Curing Rate after AnnealingCuring rate (%) after annealing=[1−(Heat generated by curing of curedresin after secondary curing)/(Heat generated by curing of curablecomposition)]×100

Exothermic Onset Temperature

Each of the curable compositions (those including the thermal cationicpolymerization initiator) obtained in the examples and comparativeexamples was heated under a heat condition below in a nitrogenatmosphere using a differential scanning calorimeter (DSC) (trade nameQ2000, supplied by TA Instruments). In this process, the heat generatedby curing of the curable composition was measured and defined as a “heatgenerated by curing of curable composition”. Based on this, atemperature at which the heat generation initiated was measured and isindicated in “Exothermic onset temperature (° C.)” in Tables 3 and 4.

Temperature Condition

The sample is held at 50° C. for 3 minutes, subsequently raised at arate of 20° C. per minute, and held at 250° C. for 3 minutes.

Time-to-Storage Elastic Modulus of 1×10⁴ Pa

Each of the curable compositions (those including the photo-cationicpolymerization initiator) obtained in the examples and comparativeexamples was subjected to UV irradiation. In this process, theviscoelastic behavior of the curable composition was measured using avisco-elastometer (rheometer) (trade name MCR301, supplied by Anton PaarJapan K.K.) and a UV irradiator (trade name LC8, supplied by HamamatsuPhotonics K.K.). Based on this, the reaction rate (curability) of thesample was evaluated. Specifically, a point at which the storage elasticmodulus reached 1×10⁴ Pa was employed as an index for a gel point. Atime from the beginning of UV irradiation until the storage elasticmodulus reached 1×10⁴ Pa was measured as a time after UV irradiation.The analysis by the rheometer was performed under conditions as follows.

Measurement mode: Oscillating mode

Measurement plate shape: Parallel (12 mm in diameter)

Measurement temperature: 25° C.

Measurement frequency: 1 Hz

Measurement strain: 0.1%

Curing Initiation Time

Each of the curable compositions obtained in the examples andcomparative examples (those including the photo-cationic polymerizationinitiator) was irradiated with an ultraviolet ray (UV), and a time fromthe beginning of UV irradiation until the phase angle began to decreasefrom 90 degrees was measured using a viscoelastometer (trade nameMCR301, supplied by Anton Paar Japan K.K.) and a UV irradiator (tradename LC8, supplied by Hamamatsu Photonics K.K.). The results areindicated in “curing initiation time (sec)” in Tables 3 and 4. Thisevaluation was performed to evaluate curability while defining an indexof the time point at which curing begins as the time point at which thephase angle begins to change (the time point at which the phase anglebegins to decrease from 90 degrees) in the viscoelastic measurement. Ashorter time as measured above indicates a shorter time from UVirradiation to the initiation of the curing reaction.

Gel Point

Each of the curable compositions (those including the photo-cationicpolymerization initiator) obtained in the examples and comparativeexamples was irradiated with an ultraviolet ray (UV), and the time fromthe beginning of UV irradiation until the phase angle reached 45 degreeswas measured using a viscoelastometer (trade name MCR301, supplied byAnton Paar Japan K.K.) and a UV irradiator (trade name LC8, supplied byHamamatsu Photonics K.K.). The point at a phase angle of 45 degreescorresponds to the intersection of the storage elastic modulus G′ andthe loss elastic modulus G″. The results are indicated as “gel point(sec)” in Tables 3 and 4. This evaluation was performed to evaluatecurability while defining an index for the gel point as the time pointat which the phase angle becomes 45 degrees in the viscoelasticmeasurement. A shorter time as measured above indicates a shorter timeto reach the gel point and a faster progress of the curing reaction.

Bending Strength, Bending Strain, and Product of Bending Strength andBending Strain

Each of the cured products obtained in the examples and comparativeexamples was subjected to bending strength and bending strainmeasurements using a tensile/compression tester (trade name RTF1350,supplied by A & D Company, Limited) in conformity with JIS K7171. Inaddition, the measured bending strength was multiplied by the bendingstrain to calculate a “product of bending strength and bending strain”.This corresponds to fracture energy. In the measurements, test specimensof a size of 20 mm long by 2.5 mm wide by 1 mm high were used.

Glass Transition Temperature: Tg

Each of the cured products obtained in the examples and comparativeexamples was subjected to a glass transition temperature measurement.The measurement was performed after a pretreatment each using adifferential scanning calorimeter (trade name Q2000, supplied by TAInstruments). In the pretreatment, the temperature was raised from −50°C. up to 250° C. at a rate of 20° C. per minute, and allowed to fallfrom 250° C. down to −50° C. at a rate of −20° C. per minute. Themeasurement was performed at measurement temperatures in the range offrom −50° C. up to 250° C. at a rate of temperature rise of 20° C. perminute in a nitrogen stream.

Linear Expansion Coefficient

Each of the cured products obtained in the examples and comparativeexamples was subjected to a linear expansion coefficient measurementusing a thermomechanical analyzer (trade name TMA/SS100, supplied by SIINanoTechnology Inc.). In the measurement, the thermal expansioncoefficient of each sample was measured at measurement temperatures inthe range of from 30° C. to 250° C. at a rate of temperature rise of 5°C. per minute to plot a thermal expansion curve, and the gradient of thethermal expansion curve was defined and indicated as the linearexpansion coefficient. Linear expansion coefficients α1 and α2 arelinear expansion coefficients (ppm/° C.) respectively at temperaturesequal to or lower than the glass transition temperature and attemperatures equal to or higher than the glass transition temperature.

Internal Transmittance

The internal transmittance of each of the cured products obtained in theexamples and comparative examples was calculated according to formulaeas follows:Internal transmittance at 400 nm=(Light transmittance at 400 nm)/(1−r)²r={(n−1)/(n+1)}²

The light transmittance at 400 nm was measured using a spectrophotometer(trade name U-3900, supplied by Hitachi High-Technologies Corporation).In the formula, n represents the refractive index at 400 nm and employsherein a refractive index at 400 nm as measured according to a methodbelow. In addition, an internal transmittance at 450 nm was alsocalculated by the procedure as above.

Storage Elastic Modulus.

The storage elastic modulus (GPa) of each of the cured products obtainedin the examples and comparative examples was determined at 25° C. by aviscoelastic measurement in conformity with JIS K7244-4 undermeasurement conditions as follows.

Measurement Conditions

Measurement instrument: Dynamic mechanical analysis (RSA-III, suppliedby TA Instruments)

Atmosphere: Nitrogen

Temperature range: −30° C. to 270° C.

Rate of temperature rise: 5° C. per minute

Refractive Index

Of each of the cured products obtained in the examples and comparativeexamples, the refractive index for light with a wavelength of 589 nm wasmeasured at 25° C. using a refractometer (trade name Model 2010,supplied by Metricon Corporation) by a method in conformity with JISK7142.

Abbe Number

The Abbe number of each of the cured products obtained in the examplesand comparative examples was calculated according to the formula:Abbe number=(n _(d)−1)/(n _(f) −n _(c))where n_(d) represents a refractive index for light with a wavelength of589.2 nm; n_(f) represents a refractive index for light with awavelength of 486.1 nm; and n, represents a refractive index for lightwith a wavelength of 656.3 nm. The refractive indices employedrefractive indices for light with the individual wavelengths as measuredaccording to the above-mentioned method.

Rate of Yellowing

Each of the cured products obtained in the examples and comparativeexamples was subjected to a heat resistance test (heat proof test) threetimes successively. The test was performed using a table-top reflow oven(supplied by SHINAPEC CO., LTD.) based on a reflow temperature profile(highest temperature: 270° C.) described in JEDEC Standards. The samplecured product after the heat resistance test was subjected tomeasurements of light transmittance and refractive indices at 400 nm andat 450 nm, thereby the internal transmittance of the cured product afterthe heat resistance test was determined, and the rate of yellowing (%)was determined based on the change in internal transmittance betweenbefore and after the heat resistance test according to the formula:Rate of yellowing (%)={(Internal transmittance before heat resistancetest)−(Internal transmittance after heat resistance test)}/(Internaltransmittance before heat resistance test)×100

The evaluation results are collectively indicated in Tables 3 and 4.

TABLE 3 Evaluation items Ex. 1-1 Ex. 1-2 Ex. 1-3 Ex. 1-4 Ex. 1-5 Ex. 1-6Ex. 1-7 Ex. 1-8 Warping after annealing absence absence absence absenceabsence absence absence absence Thermal Conversion (%) after primarycuring 94 — 88 89 88 — — — curability Conversion (%) after secondary 97— 95 95 96 — — — curing Exothermic onset temperature (°C.) 93 — 92 90 93— — — UV curability Time (sec) to Storage elastic modulus — 18 — — — 2017 16 of 1 × 10⁴ Pa Curing initiation time (sec) — 9 — — — 8 9 9 Gelpoint (sec) — 14 — — — 25 19 12 Mechanical Tg(°C.) 165-170 170-175 165154 150 168 171 148 properties Coefficient of thermal expansion a1 82 7995 91 105 109 107 129 Coefficient of thermal expansion a2 97 118 104 96117 119 117 144 Storage elastic modulus 2.50 2.60 2.19 2.27 2.17 2.102.10 1.80 (GPa, 25° C.) Bending strength (MPa, 25° C.) 105 110 108 103103 120 108 92 Bending strain (% GL, 25° C.) 3.9 4.2 3.0 2.9 3.6 4.5 3.44.2 Product of bending strength and 410 462 318 299 371 541 363 388bending strain (MPa × % GL) Cured product Internal transmittance (%) 400nm 97.9 94.9 99.0 99.2 99.0 95.2 95.0 95.0 before heat 450 nm 99.4 99.6100.0 100.0 100.0 100.0 100.0 99.4 resistance test Refractive index1.5060 1.5081 1.5118 1.5095 1.5077 1.5098 1.5097 1.5041 Abbe number 55.955.9 57.3 56.1 55.0 56.5 56.4 56.1 Cured product Internal transmittance(%) 400 nm 97.6 94.6 98.5 98.7 98.7 94.5 93.7 94.2 after heat 450 nm99.2 99.5 100.0 100.0 100.0 99.8 99.5 98.7 resistance test Rate ofyellowing (%) 400 nm 0.3 0.3 0.6 0.5 0.3 0.7 1.4 0.9 450 nm 0.2 0.1 0.30.0 0.0 0.2 0.5 0.8 Com. Ex. Com. Ex. Com. Ex. Com. Ex. Com. Ex. Com.Ex. Com. Ex. Evaluation items 1-1 1-2 1-3 14 1-5 1-6 1-7 Warping afterannealing absence absence absence absence absence absence absenceThermal Conversion (%) after primary curing 92 — 91 94 89 — — curabilityConversion (%) after secondary 97 — 98 97 96 — — curing Exothermic onsettemperature (°C.) 89 — 94 92 90 — — UV curability Time (sec) to Storageelastic modulus — 29 — — — 25 35 of 1 × 10⁴ Pa Curing initiation time(sec) — 6 — — — 7 8 Gel point (sec) — 63 — — — 69 *1 Mechanical Tg(°C.)150-155 160-165 137 164 187 177 177 properties Coefficient of thermalexpansion a1 105 93 130 125 118 97 107 Coefficient of thermal expansiona2 134 126 164 140 140 105 109 Storage elastic modulus 2.50 2.10 2.422.50 2.45 2.42 2.52 (GPa, 25° C.) Bending strength (MPa, 25° C.) 63 7873 88 76 80 77 Bending strain (% GL, 25° C.) 3.2 2.8 3.1 2.7 2.9 2.6 2.5Product of bending strength and 202 218 226 238 220 208 193 bendingstrain (MPa × % GL) Cured product Internal transmittance (%) 400 nm 95.490.1 99.7 99.5 99.2 94.7 94.9 before heat 450 nm 97.0 95.2 100.0 100.0100.0 100.0 100 resistance test Refractive index 1.5098 1.5108 1.51661.5180 1.5160 1.5160 1.5149 Abbe number 55.7 55.4 56.6 57.3 56.8 55.855.4 Cured product Internal transmittance (%) 400 nm 95.1 89.8 99.2 99.098.8 94.2 93.9 after heat 450 nm 96.5 94.9 99.9 99.9 100.0 99.3 99.1resistance test Rate of yellowing (%) 400 nm 0.3 0.3 0.5 0.5 0.4 0.5 1.1450 nm 0.5 0.3 0.1 0.1 0.0 0.6 0.9 *1: There was no intersection pointbetween G′ and G″.

TABLE 4 Evaluation items Ex. 2-1 Ex. 2-2 Ex. 2-3 Ex. 2-4 Ex. 2-5 Ex. 2-6Ex. 2-7 Ex. 2-8 Moldability Release properties good good good good goodgood good good Lens positional deviation 0.3 0.4 0.4 0.4 0.5 0.5 0.4 0.3Warping after annealing absence absence absence absence absence absenceabsence absence Thermal Conversion (%) after primary 94 — 88 89 88 — — —curability curing Conversion (%) after secondary 97 — 95 95 96 — — —curing Exothermic onset temperature (°C.) 93 — 92 90 93 — — — UVcurability Time (sec) to Storage elastic — 18 — — — 20 17 16 modulus of1 × 10⁴ Pa Curing initiation (sec) — 9 — — — 8 9 9 Gel point (sec) — 14— — — 25 19 12 Mechanical Tg (°C.) 165-170 170-175 165 154 150 168 171148 properties Coefficient of thermal expansion a1 82 79 95 91 105 109107 129 Coefficient of thermal expansion a2 97 118 104 96 117 119 117144 Storage elastic modulus (GPa, 2.50 2.60 2.19 2.27 2.17 2.10 2.101.80 25° C.) Bending strength(MPa, 25° C.) 105 110 108 103 103 120 10892 Bending strain (% GL, 25° C.) 3.9 4.2 3.0 2.9 3.6 4.5 3.4 4.2 Productof bending strength and 410 462 318 299 371 541 363 388 bending strain(MPa × % GL) Cured product Internal transmittance (%) 400 nm 97.9 94.999.0 99.2 99.0 95.2 95.0 95.0 before heat 450 nm 99.4 99.6 100.0 100.0100.0. 100.0 100.0 99.4 resistance test Refractive index 1.5060 1.50811.5118 1.5095 1.5077 1.5098 1.5097 1.5041 Abbe number 55.9 55.9 57.356.1 55.0 56.5 56.4 56.1 Cured product Internal transmittance (%) 400 nm97.6 94.6 98.5 98.7 98.7 94.5 93.7 94.2 after heat 450 nm 99.2 99.5100.0 100.0 100.0 99.8 99.5 98.7 resistance test Rate of yellowing (%)400 nm 0.3 0.3 0.6 0.5 0.3 0.7 1.4 0.9 450 nm 0.2 0.1 0.3 0.0 0.0 0.20.5 0.8 Com. Ex. Com. Ex. Com. Ex. Com. Ex. Com. Ex. Com. Ex. Com. Ex.Evaluation items 2-1 2-2 2-3 2-4 2-5 2-6 2-7 Moldability Releaseproperties fair fair fair good fair good good Lens positional deviation1.1 0.9 1.3 1.0 0.9 0.9 1.1 Warping after annealing absence absenceabsence absence absence absence absence Thermal Conversion (%) afterprimary 92 — 91 94 89 — — curability curing Conversion (%) aftersecondary 97 — 98 97 96 — — curing Exothermic onset temperature (°C.) 89— 94 92 90 — — UV curability Time (sec) to Storage elastic — 29 — — — 2535 modulus of 1 × 10⁴ Pa Curing initiation (sec) — 6 — — — 7 8 Gel point(sec) — 63 — — — 69 *1 Mechanical Tg (°C.) 150-155 160-165 137 164 187177 177 properties Coefficient of thermal expansion a1 105 93 130 125118 97 107 Coefficient of thermal expansion a2 134 126 164 140 140 105109 Storage elastic modulus (GPa, 2.50 2.10 2.42 2.50 2.45 2.42 2.52 25°C.) Bending strength(MPa, 25° C.) 63 78 73 88 76 80 77 Bending strain (%GL, 25° C.) 3.2 2.8 3.1 2.7 2.9 2.6 2.5 Product of bending strength and202 218 226 238 220 208 193 bending strain (MPa × % GL) Cured productInternal transmittance (%) 400 nm 95.4 90.1 99.7 99.5 99.2 94.7 94.9before heat 450 nm 97.0 95.2 100.0 100.0 100.0 100.0 100 resistance testRefractive index 1.5098 1.5108 1.5166 1.5180 1.5160 1.5160 1.5149 Abbenumber 55.7 55.4 56.6 57.3 56.8 55.8 55.4 Cured product Internaltransmittance (%) 400 nm 95.1 89.8 99.2 99.0 98.8 94.2 93.9 after heat450 nm 96.5 94.9 99.9 99.9 100.0 99.3 99.1 resistance test Rate ofyellowing (%) 400 nm 0.3 0.3 0.5 0.5 0.4 0.5 1.1 450 nm 0.5 0.3 0.1 0.10.0 0.6 0.9 *1: There was no intersection point between G′ and G″.

INDUSTRIAL APPLICABILITY

The curable composition [1] according to the present invention ispreferably usable as a material for optical element formation (as acomposition for optical element formation). The curable composition [2]according to the present invention is a curable composition that issuitable for the formation of a wafer-level lens (as a curablecomposition for a wafer-level lens).

The invention claimed is:
 1. A curable composition comprising: acycloaliphatic epoxide (A); a siloxane (B) comprising at least two epoxygroups per molecule; a curing agent (C); and a hydrogenated glycidylether epoxide; wherein the siloxane (B) is one or more compoundsrepresented by the following formulae:

wherein the content of the hydrogenated glycidyl ether epoxide is 5 to40 percent by weight based on the total amount (100 percent by weight)of curable compounds contained in the curable composition.
 2. Thecurable composition according to claim 1, wherein the cycloaliphaticepoxide (A) comprises a compound represented by Formula (I):

wherein X is selected from a single bond and a linkage group.
 3. Thecurable composition according to claim 1, wherein the siloxane (B)comprising at least two epoxy groups per molecule comprises acycloaliphatic epoxy group as at least one of the epoxy groups.
 4. Thecurable composition according to claim 1, wherein the curablecomposition comprises the cycloaliphatic epoxide (A) in a content offrom 5 to 60 percent by weight based on the total amount (100 percent byweight) of the curable composition.
 5. The curable composition accordingto claim 1, wherein the cycloaliphatic epoxide (A) comprises 3,4,3′,4′-diepoxybicyclohexyl.
 6. The curable composition according to claim 1,as a composition for optical element formation.
 7. The curablecomposition according to claim 1, as a composition for a wafer-levellens.
 8. A cured product of the curable composition according toclaim
 1. 9. An optical element comprising a cured product of the curablecomposition according to claim
 6. 10. An optical device comprising theoptical element according to claim
 9. 11. A method for producing awafer-level lens, the method comprising subjecting the curablecomposition for a wafer-level lens according to claim 7 to one of castmolding and injection molding.
 12. The method for producing awafer-level lens, according to claim 7, wherein a cast molding or aninjection molding comprises the steps of: 1a or 1b) preparing awafer-level-lens mold comprising at least one lens pattern; 2a or 2b)bringing or injecting the curable composition for a wafer-level lensinto contact with the wafer-level-lens mold; and 3a or 3b) applying atleast one of heat and light to the curable composition for a wafer-levellens to cure the curable composition to thereby give a cured product ofthe curable composition.
 13. The method for producing a wafer-levellens, according to claim 12, wherein the cast molding or the injectionmolding further comprises, after the step 3a or 3b), the step of 4a or4b) annealing the cured product of the curable composition for awafer-level lens.
 14. The method for producing a wafer-level lens,according to claim 12, wherein the cast molding further comprises, afterthe step 3a), the step of 5a) cutting the cured product of the curablecomposition for a wafer-level lens.
 15. A wafer-level-lens sheetobtained by the method for producing a wafer-level lens according toclaim
 12. 16. A wafer-level lens obtained by the method for producing awafer-level lens according to claim
 11. 17. An optical device comprisingthe wafer-level lens according to claim
 16. 18. A wafer-level lens stackcomprising a plurality of wafer-level lenses, the plurality ofwafer-level lenses constituting the stack comprising a wafer-level lensobtained by curing and molding the curable composition for a wafer-levellens according to claim
 7. 19. A curable composition, comprising: acycloaliphatic epoxide (A); a siloxane (B) comprising at least two epoxygroups per molecule; a curing agent (C); a hydrogenated glycidyl etherepoxide; and an oxetane compound; wherein the siloxane (B) comprises acyclic siloxane and that the cyclic siloxane comprises 4 to12 Si—Ounits, wherein the content of the hydrogenated glycidyl ether epoxide is5 to 40 percent by weight based on the total amount (100 percent byweight) of curable compounds contained in the curable composition, andwherein the content of the oxetane compound is 5 to 30 percent by weightbased on the total amount (100 percent by weight) of curable compoundscontained in the curable composition.
 20. The curable compositionaccording to claim 19, wherein the cycloaliphatic epoxide (A) comprisesa compound represented by Formula (I):

wherein X is selected from a single bond and a linkage group.
 21. Acurable composition comprising: a cycloaliphatic epoxide (A); a siloxane(B); a curing agent (C); and a hydrogenated glycidyl ether epoxide;wherein the siloxane (B) is represented by Formula (1)

wherein R¹ and R² are, independently in each occurrence, selected fromalkyl and a monovalent group containing a cycloaliphatic epoxy group,where at least two occurrences of R¹ and/or R² in the compoundrepresented by Formula (1) are each independently a monovalent groupcontaining a cycloaliphatic epoxy group; and q represents an integer of3 or more.
 22. The curable composition according to claim 21, whereinthe content of the hydrogenated glycidyl ether epoxide is 5 to 40percent by weight based on the total amount (100 percent by weight) ofcurable compounds contained in the curable composition.
 23. The curablecomposition according to claim 21, wherein the cycloaliphatic epoxide(A) comprises a compound represented by Formula (I):

wherein X is selected from a single bond and a linkage group.